c: Glad you decided to ask me questions because, unlike you, I FULLY plan to answer them.
Who says that marksmen aren't viable?
No one but cold hard statistics. The bottom winrates on OP.GG for bot lane are currently as follows, starting from the lowest percentage and going to the highest:
Varus (42%)
Lux (45%)
Caitlyn (45%)
Tristana (45%)
Xayah (46%)
Vlad (48%)
Kog (48%)
Sivir (48%)
Kai'sa (48%)
Kalista (48%)
Ezreal (48%)
Darius (49%)
Vayne (49%)
Brand (49%)
Lucian (50%)
I highlight Lucian because he's the first ADC out of ten ADCs to have a 50% winrate. That means that the majority of the ADC class is losing more than 50% of them games in the one lane that they were actually balanced for; in the one lane that they can actually go to. These are not without substantial pick rates and this is at Korean Plat + so it isn't just players being bad at the game. Of the bottom five winrates of the lane, four are ADCs and they all four have critically bad win rates.
Before patch 8.11 hit, the role did not have this huge of a variance in win rations between its lowest winrate champions and its highest with this staggering number of champions at a sub 50% winrate.
Even just ignoring these win rates, however, there is also the fact that many LCK teams have started opting to not pick marksmen at all in their professional games. While I do not put much hold on pro game picks, a lot of other people do and seem to believe that professional level is how the game is meant to be played. And in a way, it is. It is meant to be played with a team with whom you have repertoire and synergy with and its meant to be a more strategic endeavor with actual picks and bans being based around the comp you wish to make. The only thing is you just won't get that in soloqueue. But I digress, if pros aren't even picking marksmen in their games and are playing full melee teams(something that's never happened before now), then there is clearly an issue of viability with the champions.
Who says you can't play marksmen top, mid, jungle?
No one except your team and the fact that most of the crit marksmen are ill adapt at going anywhere bot botlane, doubly so after their health regen stat got nerfed. It makes it a little hard to go mid against pokey assassins and mages if you don't have the health regen, base armor, or MR to survive their onslaught. Or its hard to go top against a bruiser or tank that can all in you level 3 because you're immobile, need items to do damage, and have no forms of self peel. And again have no armor, health regen, or MR to survive the encounter. And clearing the jungler is difficult when you only have single target clears, low sustain due to having your one sustain keystone nerfed and, again, no health regen, and a weak dueling potential making you extremely reliable on your laners to have lane priority when going for scuttle crabs.
So nothing stops these champions from going mid, top, jungle beyond their own inability to optimally survive there where as mages/assassins/bruisers/tanks have always had the ability to go bot and never had a good reason not to. Mages can team up with an aggressive support and easily poke out the squishy, low damage early ADC and use the range of their spells and the threat of an eventual all in to force them back. Bruiser/tanks/assassins can just do the same thing that they did top/mid lane; get to level 3 and proceed to all in, especially if they have an all in support or a poke support. And all of these champions have higher base stats, higher base damages, and better and faster builds and powerspikes than ADCs. There was never anything preventing them from going bot beyond that they could also go to a solo lane and not have to be behind in levels.
Not only that but there are only around 20 marksmen and yet Jinx,Jhin,MF,Lucian,Kai'sa and Twitch are all champions who ACTUALLY ARE VIABLE WITH OVER A 50% WR! Ezrael is the only one with a 47% wr and that is most likely because his very high pickrate.
So out of 20 marksmen, five are viable. 25% of a roster is viable. That's some good odds right there. :') Glad I have so much diversity as an ADC main. As for Ezreal's WR, its not because of his high pick rate; he had a high pick rate the previous patch and the patch before that and the patch before that; his pick rate never affects his winrate. He's one of those ADCs that people play no matter how good or bad he is because he's an especially favorite ADC; before this current patch right now, he had a +50% winrate. Riot just gave him further base stat nerfs to bring him further in line.
You just have to look at the graphs of playrates in botlane and you'd see that most people actually pick ADC's.
Pick rate=/=Viability.
People still picked bruisers when they were apparently "unviable" because that is what they wanted to play. ADCs are the same way; they will always be picked regardless of viability and regardless of whatever bullshit "diversity" people try to shove botlane because that's what people who play bot lane want to play. They started playing bot lane specifically because ADCs are what they wanted to play botlane. So of course ADC's pick rate is not going to go down; just because you nerf an entire class of champions does not mean that the people who enjoyed playing them is going to magically stop playing them. They play those champions because that's what they enjoy playing. In the same way that Mages are apparently shit right now but you still see people playing mages nearly every game or every other game on one team or the other. Viability does not and never will equate to play rate and the sooner people get that into their thick skulls, the better off everyone would be.
Also you didnt quite understand my question. What I meant was more like ''why was it okay for almost all bruisers to be shit in almost the entire S7 but now that crit adc's are strugguling it isnt okay anymore?''
If that's what you meant, then that's what you should have asked. The fact of the matter is, Bruisers were not shit in almost all of S7. From my understanding, in S7, they were in a fine state. I saw plenty of Renektons, Dariuses, Fioras, Jaxes, Kleds, Gnars, J4(he was even a flavor of the month), Wukong, Camille(does anyone remember Camille? Oh god Camille...), Nasus, Warwick... The list goes on and on and on. They were played frequently and I rarely saw complaints that they were unviable or unplayable. Furthermore, they actually had a keystone then that wasn't completely broken and had a clause specifically in it for them to allow them stack it up and use it faster; Fervor of Battle was actually a good mastery/keystone/what have you and I never saw bruisers complain about it once.
The beginning of season 8 they were bad for three or four patches because, somehow, Riot over looked giving them a keystone that was meaningful. They rectified this a little too aggressively in my opinion as Conqueror is an over tuned piece of shit that only they can use worth a damn. They should have just returned Fervor of Battle and taken out PTA and Conqueror. Giving flat AD instead of increased damage from all sources or flat out true damage is far better and healthier for the game. :/
Also dont spew bs botlane was generally the 2nd most picked role until 8.11.
I do believe that's what I said. I said that before 8.11, ADC was actually even with mid and only slightly ahead of jungle and top which were both tied. And then I followed it up with post 8.11 the role has dropped drastically and no one plays it. There is no BS in this statement as yourself just admitted that it is true. That botlane mains are now dropping and fleeing the role as a whole. So thanks for agreeing with me.
guardian angel offers 45 AD and 40 armor while also increasing your health value by 50% for a price CHEAPER than static shiv or bloodthirster
(all of them picked in pro) 
(and those have good stats in soloq)
Support and my premade is playing 
ADC ( well, she builds AP, of course, and so do I ). I feel like it's legit.
Support, even going as far as doing good in a 3v5 situation. ( it was on PBE, and our 
midlane and 
toplane both ragequited )
one day.
