The League of Legends hivemind can be a very, very strange place at times, especially when it comes to patch changes. Things that get even the slightest nerf are often immediately considered trash, only to come back into vogue very shortly after when it becomes obvious that the nerfs were far less deadly than initially suspected. When it comes to new champion releases, this effect is particularly egregious, as players abandoned both Camille and Ivern en masse after their most recent round of nerfs, at least for a week. Fast forward a bit and Ivern is still the most dominant solo queue jungler in the game, while Camille is still permanently banned in nearly every competitive game and has single-handedly brought Renekton back into the metagame thanks to his ability to check her during the early game.
Thus, I can't say that I'm surprised about the reaction people seem to have had to the Exhaust nerf in patch 7.5. Yes, the fact that it no longer shreds 10 armor and mr is an annoyance. Yes, the fact that it no longer slows attack speed means that Kalista gets to be a champion again. Objectively speaking, Exhaust is now a worse summoner spell than it was back on 7.4. I don't disagree with that.
Prior to patch 7.5, however, Exhaust was the best non-Flash summoner spell in the game by a very wide margin. Trimming off some of the less relevant parts of the summoner spell isn't going to change that. Syndra can have all the attack speed she wants but Exhaust will still top Unleashed Power from one-shotting anyone your team like it normally does. Caitlyn might be able to auto at the normal speed, but she's still a sitting duck while exhausted since she's still slowed and still deals 40% less damage than she would otherwise.
The reality is that League of Legends has turned into a very caster-centric game for quite a while now. The best ADCs have, for the last few months, been those that really on their spells for damage and not a long string of autoattacks. If you count Lucian in that former camp, then those "few months" instead turn to "few years". Today's game is also dominated by junglers like Graves and Kha'zix, both of whom can't do a darn thing while their under the effects of Exhaust. And if I need to explain to you exactly why Syndra, Zed, or Veigar don't like being exhausted, you may need to reread exactly what the summoner spell does.
Exhaust removes a target damage-dealing champion from the game for 2.5 seconds. That's the long and short of it. If that doesn't sound like one of the best things you can be doing in League of Legends the by all means, start taking Ignite every game instead, or whatever other spell suits your fancy if you're a mid laner. When the fed enemy Talon, Zed, Ahri, etc. kill you by looking at you funny, though, remember that you chose the path you're on. Nothing makes a fight easier to win than making a 4v5, and that's exactly what exhaust can do. No other spell offers anything close to that save Flash or Teleport. If you like LP, keep taking Exhaust and keep punishing overeager assassins.