I don't think it's the bara factor itself that pisses people off, but rather how slipshod its implementation into the Litten line was.
The only baramon that really pissed everybody off was Incineroar, and I think that's mostly because it went from a quadrupedal cat, that wasn't humanoid at all, to blatant bara furbait that looked nothing like it except for the colour scheme. The progression wasn't as bizarre and random with Marshstomp, who isn't that humanoid and still walks on all fours, and Chesnaught, who began pretty humanoid and was also meant to be a reference to an RPG archetype. Both of those lines still retain the character of the first stage pretty well; Marshtomp in particular is very obviously Mudkip's last stage, and Chesnaught - although it has kind of a shitty design - was thematically in keeping with the rest of its stages.
The Litten line is one of the most astringent, jarring progressions in Pokemon history; it's almost on the level of Remoraid - Octillery.
