you are sacrificing either speed or power. swellow and zangoose do not have to do that. in fact, guts swellow still outspeeds quick feet ursaring who only hits 343 speed with a jolly nature. on the other hand, zangoose only falls a little short of that speed, but does not suffer from that significant loss in power. regardless, swellow and zangoose both have access to quick attack and good speed with their damage-output-boosting abilities; orb ursaring is just outclassed. 3HKOs are not ideal because many things in the tier just 2HKO or OHKO back. you need to provide a more sufficient argument for that. sealeo takes hits and then what? it was just setup fodder for musharna from what you described. sealeo may be able to take hits, but there are many cases in which it will not do sufficient damage in return or will run into trouble with calm mind pokémon. your scenario there showed a reason why sealeo is not worthy of a d rank, and i do not see why that should be used over something such as regice which sports better bulk and access to thunderbolt.