Sure. But let's be honest: almost every GM has at least a couple of house rules, or leans towards certain interpretations of RAW.
Oh, certainly. But most of those houserules and interpretations are minor -- designed to remove an OP build, or clarify a complicated rules question. I wouldn't say they provide much GM flavor, and I also wouldn't say they should.
It's just a rather absurd thing to say imho that a GM is 'transparent' and should leave no imprint on the game. TTRPGs are hugely flexible, subjective and complex beasts that have the GM's fingerprints all over every session. In a literal sense the point of the game is for it to reflect and extend the personalities of the GM and players. Otherwise you may as well play a video game.
I'll agree with that when it comes to setting and story. But rules-wise? I see no reason why the GM and the players shouldn't try to be as transparent with the rules as possible.
Sure, the GM is going to leave his interpretation and views on everything he touches. And so should the players.
Transparent rule management leaves more room for the players to place their own fingerprints on the game. It means both 'sides' are working from the same baseline, so neither can bend or change the story independently from the context of the rules, and thereby overrun the others' contribution.
And that's really where TTRPGs are advantageous, compared to playing a video game, or cooperative novel writing, or whathaveyou -- the ability to provide a level playing field where all members can leave their mark without stomping over each other.