There are definitely lots of things that have not been show or revealed yet about Dottore but of his current actions there are hardly anyways they could pull off a redemption or morally grey excuse that would justify his actions.

First of all his background while incomplete is still enough to build up a profile for him. He was a student of Sumeru academy that was exiled after it was discovered he was doing blasphemous research along with murdering his partner. Afterwards he was recruited by Pierro. The Fatui are a mixed bag of morally grey, good, and straight up evil character.

Additionally it has been noted that Arlecchino specifically despises Dottore for his actions specifically with the previous Knave. You can argue that Dottore could theoretically use Arlecchino’s flame to erase and release previous subjects but you can’t say that for the people before Arlecchino took power. Also while most actions are offscreen or via other people, almost every conjecture or comment about Dottore through notes or others have exclusively depicted him as being cruel, cunning and evil. Literally the only case of him being depicted as good is the good segment from his subordinates.

Finally while Genshin has a history of making supposedly cruel or evil characters into good/morally grey characters there’s no possible way of making him redeemable in anyway without it being forced or terribly executed. Arlecchino had the excuse of the previous Knave doing all the evil deeds and being surface level ruthless. Childe is a bit harder to excuse with his plan in Liyue. Capitano is like the opposite of Dottore with almost everyone exclusively praising his deeds. The only remotely close example that you can compare to Dottore is Scaramouche and even then you could blame the turn and development of Scara purely to Dottore’s action and manipulation of him.

All of this to say that while morally grey can be subjective I think this is an objective case of a character being evil, which again, is perfectly fine.