FWIW, Hecarim and Udyr each received several nerfs in addition to Chemtank being nerfed.
I know Reddit likes to complain about "triple nerfing" something, but sometimes that doesn't do enough.
Hecarim's nerfs weren't in for the LCS playoffs, though he was still #1 pick/ban in the 11.6 playoffs regions.
Hecarim's second nerf, Udyr's third nerf, and Chemtank's nerf were all in 11.7, which were all put in after Riot reacted to the 11.5 second round of Udyr nerfs not lowering his priority enough.
I think a third hit on Hecarim in 11.8 is warranted, but it's not like Riot didn't continually tap them down.
Plus, let's not act like pros are good at reacting to changes on time. You say "months ago" as though people whose literal job it is to pick the strongest champions didn't fail to identify them.
11.2 had Chemtank's big buffs where it got much cheaper. Hecarim's presence: 28%. Udyr's was 74%
11.3, where Udyr was specifically nerfed and Hecarim was unchanged: Hecarim to 41% and Udyr shot up to 91%.
11.4, pro teams still catching up: Hecarim to 61%, Udyr still at 92%
11.5, pro teams still catching up (and the second round of Udyr nerfs): Hecarim to 97% and Udyr falling to 84%
11.6, the first Hecarim nerf of the year since his pro presence had been pretty low up until recently: Hecarim 95%, Udyr 80%
And we don't have pro play on 11.7 yet, which has further nerfs to both Udyr and Hecarim as well as Chemtank.
So what did we observe today? Hecarim in his strongest state took a full two months for pros to react. Udyr still had a couple patches of lag for all teams to catch on. What makes you think they're going to be any better at this on the way down?
Udyr's presence is already declining after the (edit) second nerf he received. It's reasonable to assume the further nerfs in 11.7 are going to take him off of his pedestal. The champion's solo queue win rate is completely reasonable and at this point a high ban rate is people being unwilling to accept that he's fine now and they should just deal with the fact that he kinda jungles fast.