Worst recovery of any lightweight imo. Other characters with similarly vulnerable recoveries can, at times, trade damage for survival, but Squirtle is like 2nd lightest in the game.
As for camping, yea his movement is still stellar when fatigued, but with less damage (and thus less priority?) its alot harder to hold a lead and stay a threat to your opponent. Less hitstun on things like ftilt, jab combos (doesn't even work properly anymore once fatigued?) and all of your kill moves being much weaker, its a tough spot to be in.
Weighing that against being "pretty good" for 70ish seconds and it doesn't look so great. Especially when you factor in the other 2 that would be solidly low tier without question.
EDit- mid tier is more fun than low tier, and I do agree that PT puts some major hurt on most of low tier, despite that i feel pt is low tier overall.