Steelix can be easily countered, making its tankiness basically useless in the meta.
I agree that Crunch Tyranitars can be at near the top of the list, but Stone Edge ones can be really far behind, not to mention Fire Blast. Just throw in a Machamp and Stone Edge would probably never be released.
Hydro Pump Gyarados lol, that was before the gym rework, I wonder why it is still the A moveset. Crunch is better, and Outrage ones can be even "anchored" by Charge Beam Clefables.
Rhydon is a great defender, maybe, but Vaporeons and Exeggutors can demolish it before being able to use Stone Edges.
Why is Espeon on the list? Just throw in a Mewtwo counter and destroy it. Alakazam, makes more sense, since the candies are much harder to come by, but still same reason as Espeon, gets destroyed by Mewtwo counters. Same fate on Hypno, despite being strictly tankier.
Psybeam on Chansey deals laughable damage to Tyranitars, Houndooms, even Murkrows!