But yeah, I agree with Kanghas being UU... It has a whopping 295 attack. It has nice moves but doesn't hit too hard.
It's not only base 95 attack (which gets you to 317 if you're using a boosting nature, btw). Kanga's also got 90 base speed, very bulky stats for UU (105/80/80 - in terms of SkarmCents, that's bulkier than Quagsire), and a huge offensive movepool which includes Return, Sucker Punch, Crunch, Earthquake, Hammer Arm, Focus Punch, and Fake Out. With Return, Earthquake, and Sucker Punch/Crunch, it hits everything in UU that resists normal SE (the one exception being Wormadam Trash, who isn't a great pokemon in itself and who also lacks a way to really threaten Kanga).
Furthermore, Kanga is only weak to fighting, and no UU Fighting pokemon except Hitmontop (and Wrath if it remains UU) can safely switch into Kangaskhan. All UU Fighting types except Primape are slower than Kanga, as well. Top is slightly sketchy - a fully defensive top (252/252 Impish with Intimidate) takes
36.84% - 43.42% from an Adamant CB Return,
24.67% - 29.28% with no boosting item. With just 4 attack EV's, however, Top only has about a 8% chance of OHKOing a 4/0 Kangaskhan with CC. Since Kangaskhan outspeeds Hitmontop, it can easily KO it after the defense drop unless Top is packing Mach Punch. Either way, Hitmontop lacks reliable recovery and stands a chance of being KO'd after 3 switch-ins - residual damage means it almost certainly loses. Top does stand a decent chance of beating Kanga, but it's still not a 100% counter and gets worn out after switching in too many times anyways.