That certainly helps! But things of course can be represented in different ways, not necessarily by acting, it can be also via evocative descriptions and other storytelling techniques. But yeah, if the GM cannot evoke genuine feeling in the players somehow, they will never be a very good GM. Like imagine watching a movie that did not evoke any feelings in you. What a drag.
Well, if they are it will certainly make that game more enjoyable to everyone. But the reason for asymmetry is the different knowledge sets of participants. The player probably knows more about their character than the GM of the NPC, meanwhile the GM knows massively more about all sort of things the NPC would not know about. Like the player can be genuinely misled by the NPC, but the same simply cannot happen in reverse.