Mega Kangaskhan is on another level compared to the rest of the Megas and most have Power-Up Punch+Sucker Punch on their set, so dealing with Rock/Steel is no biggy while for Fighting, it has Return.
Anyway, Swampert's lack of recovery, lowers its tanking abilities, it's extremely susceptible to all types of hazards, so tanking is further nullified, below/slow speed, average SpD for a supposed tank. Look, if Blaziken gets Speed Boost TWICE, why not give Swampert some love with Sap Sipper (it truly was not my first ability of choice for it, but whatever).