The reason why we dont see that many Assassins in proplay is because they somewhat requiere to get ahead somehow to get snowballing and thus take over the game. Proplayers are good enough to minimize the snowball oppertunitys and also are coordinatated enough to fight of assassins in teamfights.
Iginte gets you way easier snowballing, but cleanse helps you to counter exhaust, which counters your snowball.
So you can pick easier/faster snowball or safer/reliable snowball when you get snowballing.
We are in a Burst Meta, not an Assassin Meta. Assassins burst, Poke burst, Mages burst(mostly), even tanks/offtanks have a decent burst.
And then use the 5v4 that you created with your burst to take objectivs and win the game.
If we make it harder to burst people, aka. reducing the overall dmg or strengthen towers so they are not made out of paper anymore... This would make games longer and less snowbally, so you simply cant burst your enemy as easily anymore.
You pick an assassin to kill your enemy in the midgame, which starts around level 7+ or your first complete item.
You dont pick them for a good lategame aka. good teamfights. You pick them to snowball and rofl over your enemy. And exhaust tries to counter that, but you can also counter exhaust with cleanse. So its even and doesnt justifiy to nerf exhaust. Even if they only nerf it against adcs.
If they wanted to buff adcs, make the games less snowbally/longer.
So it doesnt makes sense to me to nerf it!
And Assassins already got the insane EoN, which counters their biggest weakness: CC.
It was 100% clear that it was to strong back then and they even buffed it later xD
I said that already when EoN was released...
So to bring everything together: There is to much burst everywhere, be it assassins or mages or whatever.
And there is no real reason for this exhaust nerf.
If it was targeted to help adcs, than it definitly was the wrong aprotch.