You never said any of those things, or at least not with those words so the quotes make no sense, yet i don't even see such sentiments being made in your previous comments.
At best, you said when playing tanks "you have time on your side", which doesn't mean much, because more time for you also means more time for the enemy.
Assassins don't normally lose from a single mistake. On the contrary, because of how many defensive mechanics they are often given, zed teleports, LB teleports, ekko ult, yasuo shield (he's in blood moon so he somehow fits "assassin power fantasy" smh), fizz E, akali W, rengar W, kha ult, kat shumpo resets. These are all mechanic which act to reduce punishment for misplays, they're not intended to be used in such a way, but it's difficult to make a skill which lets a champion escape after an assassination, which doesn't double as a defensive mechanic.
Now, there is validity to the idea that a single mistake usually means they lose, however, it's a mistake that's made only after their "OOPS button" has been exhausted. Where as other champions aren't given these defensive mechanics will die to assassins very easily, not because they misused their defensive CDs, but because they didn't have one or the assassin can play around such skills to still get kills, where as very few champions can actually play around the defensive skills that assassins are given in a way which still rewards a kill. Most of the time it has to do with DoT damage.
Now, tank fights do require more "dancing" as you put it, however given that tanks are often given quite a bit of stick. Misjudge their power and try to fight, you will get hurt. Avoid a fight, and they have a hard time forcing a kill onto you.
Champions with high burst, such as assassins, are the opposite of this. Where if you misjudge their power, then you have almost no chance of not dying or getting dangerously low. Yet once they've gained a slight lead, they have a very easy time threatening you, despite your attempts to avoid fighting.
It sounds counter intuitive, but being able to stall, actually increases how much people will fight and take risky plays. If i'm fighting someone that i'm worried about getting knocked out by, i'm going to make fewer attacks to avoid substantial punishment for a mistake. Mind you this has less to do with how well i can take a hit and more to do with how powerful of a blow they can deliver, because even if it wouldn't knock met out, risking injury from a single blow is just as dangerous.
Where as if i'm fighting someone who i'm confident a single mistake will not heavily punish me, i will fight more aggressive making more risky and more flashy moves in order to try and gain as much advantage as possible and find a gap in their defensive knowledge, or even make them build up a habit and then make a decisive play around that habit (i'm not even talking about LOL anymore, i'm talking about actual competitive fighting, taekwondo in my case).
This is just a rant/story explaining why it's far more interesting to have extended fights.
There was once a match where i intentionally did nothing but fight off of my front leg, which is faster, disruptive, and less taxing on the body to do (i only had a 1min breather between this match and my next). I'm a very proficient back leg fighter still, though not quite as much as my front leg, but there was strategy behind not using everything at my disposal. In the last 5 seconds of a fight I took advantage of a habit I had tricked my opponent into, where he would put his full guard onto the side which my leg was forward (this could've subconscious or a conscious decision). Five seconds left, down 1 point, I turned over into a powerful back leg roundhouse, which he was completely defenseless against, and scored the two points i needed to win, and nearly knocked the guy out by accident, something I done before but didn't want to do unnecessarily, but was intentionally trying to stun him for the rest of the time.
That whole match i gave up ground, on the basis that by the end, i'd likely have the element of surprise on my side to make a decisive play.
Competitive fighting is like flesh chess. This is what makes extended fights interesting even in league. You can make strategic plays that cost you, with the goal of delayed benefits.