I agree, perhaps what people see as noble in him is that he is incorruptible when it comes to his own moral code. I always think of noble gases when I hear "noble" xD so something that doesn't mix. And I think that's right for Garak. Noble as in righteous definitely is not fitting.

He is an incredibly likeable character, but just because that's a part of his skillset!

We shouldn't forget that he believes cruelty can be justified, like most Cardassians seem to do. Either a lot of people agree on this take on cruelty, or it's easy to forget because in the show his cruelty is rarely shown. We just hear about it (mostly).