So let me see if I have this straight. Robb Stark won every battle he was ever in (as a teenager!) and had his vassals conspiring against him from the get go as he was considered “weak” Mace Tyrell “won” one battle in his life (that he didn’t personally show up for) but none of his bannermen (including noted warriors like Tarly) will lift a finger against him AND he has a rep as a great warrior. Something’s missing here…

Bolton’s something of an outlier here, but I wouldn’t say that he has them “conspiring against him from the get go.” Rather, they’re looking to see what kind of advantages they can get from him – Greatjon wants command, Manderly wants a mint, Cerwyn and Mormont are interested in marriages, Hornwood wants lands and privileges – because he’s a new commodity.

Mace is a known quantity, and while he’s a bit of a doofus, he has a decent command of feudal politics. Randyll Tarly gets the military commands, his mother is a Redwyne and his sister married the Lord of the Arbor, the Fossoways get a marriage to Garlan and his other sister, he’s married into the Hightowers, and so on and so forth. So he’s got a good constituency behind him. However, I will note that House Fossoway, House Florent, House Willum, House Varner, House Crane, etc.. all abandoned Mace the moment Renly died.