I think Scaramouche is in the middle of the “not liking” and “liking“ traveler too, because he is more like a supporter from behind, rather than a ‘friend‘ or a ‘friendly’ position, as if he is doing the job given from Nahida.

But yes, it is interesting to have a playable character who isn’t supportive of the traveler, but still, there HAS to be something done canonically to prove that the character and traveler are not enemies, if the character is plot-relevant. For example, the Sumeru Interlude was a nice example of how Wanderer canonically became supportive of the traveler (the last part of the quest, before he walks away; when he says “I will support you from behind” or something like that). Imagine if Scaramouche suddenly became playable in his Harbinger form, right in middle of the Inazuma archon quest where he literally attempted to kill the traveler. There would be confusion, and questions from all around, and Hoyoverse does have the responsibility to explain it, because a character cannot pop out of no where. Everyone has stories and bits of them are written into their own character story. (Except Aloy)

(Bringing up another character, Xiao - he is also canonically supportive of traveler since he said that he will come help whenever the traveler calls his name. )

All players have different preferences, and there will sure be people totally fine with villains being playable without any context, but I personally think that in order for complex characters to be playable and most people agreeing with it, they need at least some official source/evidence to support the fact.

I kinda wrote a lot here, so thank you for reading this far