the current state of balance...
As everyone knows, game has becoming faster and faster in terms of game pace. It was common that game end around 30~40 minute prior to the preseason, the preseason patch has made the game into 20 minute or so snowball game.
I saw someone had a post on what you can do when the enemy got ahead/ snowball. the post has empty content... I have to agree, you can do nothing...
The benefit high tier item provide alter the game too much. During the laning phase, when enemy won a fight and bought a pickaxe or zeal, it was still alright you can still attempt a trade and perhaps win in some way. But when they hit the item like RF cannon or shiv? You get punished really hard. Not only does the item provide the basic stat (atk spd or ad) they get and extra proc of attack. If your support don't land a amazing cc or have jungle ganking for you Properly, you have almost no chance in winning the fight. "oh, just farm up... catch up and stuff..." like your opponent isn't farming or taking other objective as well. Not to mention he can zone you out if he decides to farm as well... he will get more farms than you do while the difference in gap just get larger and larger.
the extra damage mastery keystone provide making a comeback even harder. While mastery provide extra damage is cool at first glance, it become another source of snowballing. As your opponent gains a level advantage on you, he deals even more damage now then previous patch. Let's be honest here, we are talking about the thunderlord's decree, that's what almost everyone uses now. Team thunderlord is not all that uncommon... You lose one fight, he gets a 300 gold advantage, as well as 10 + x more damage from bonus stat from level and item. What can you freaking do??? Even if you out farm him slightly (assuming both player have equal skill in farming) you will still be at a horrible disadvantage. Not only does he get better stuff (fine, that's what you get for winning) but the mastery also deals more damage than yours, making trade extremely unfavorable.
Traditionally when you lose fight, you will be buying defensive item. But the additional damage on item deals such as shiv and cannon makes you wonder what do you even buy?? items ad champion buys deals ap damage? better get more damage to have better chance at hoping to win a fight...
Not to mention riot removed the green ward from purchase list. You can't even have vision when you need it half the time... making losing side play even more passive. allowing opponent to roam easier.
There are so little chances to make a comeback now... if anything it will be having a support like thresh or blitzcrank land an amazing hook or have champion with complex mechanic like lee sin to pull a insec that can turn the tide (but if your team dont have such champion and they arent good? better luck next game). League has become so one-sided once one side have taken some sort of advantage... that you might as well all afk...
Honestly I was going to rant just about the thunder lord's decree... but I guess i expanded a lot more...