Extra content doesn't justify fucking up with the speed. It all started because they had shitty animations and gameplay felt clunky without high speed and it ended up in retardo land.
Clear speed should be a reward for completing your build. In PoE atm 1 shotting standard packs is a minimum requirement. At any point in the game you can chose the difficulty and the way rewards are tuned extremely favors you chosing a difficulty where your build 1 shots.
Oh and I almost forgot the rares. The difference is so big that if you go to a difficulty where normal mobs have any meaning there's a big chance the rares fuck you up. So no, it's not as simple as "gimp yourself" when for some years now their design decisions are done for retardo mode. Same applies for league mechanics.
Everything you said is wrong.
GGG didn't fuck up with speed, speed is what the players want.
Animations are tied to attack and cast speed, not clear. Clear is scaled by explosions, proliferations, extra projectiles etc.
Clear being a reward for "completing" a build is the second most retarded suggestion I've heard from you. Why the fuck would a boss killing char need clear speed? Why would a Lab running build or Heist running build need clear speed?
One shotting normal packs isn't a requirement at all. Most league starter builds have to use at least two skills to clear a pack.
Rewards aren't tuned for clearing packs in low tier content. Rares drop the big loot now. They have been doing so for a year+ now. If you haven't played in a while, maybe shut the fuck up.
Speaking of Rares, if you don't invest into clear speed but still struggle with Rares, then what the fuck are you investing in?
My top character this league is a brand grandpa who isn't very fast and doesn't have good clear (until I found an Inpulsa at lvl99), but he is very tanky and has great single target. If you can't build a non-zoom character without "gimping" yourself, then that is your problem. The game gives you plenty of options.