If it had been a peacetime transition, I don't think Ferid would not have been as well-liked as he was when Armes invaded.
Now I don't think everyone would have disliked him, he does have that Egan charisma so he'd still managed to draw some folk in. Without it, he would've likely found favor with Raftfleet, the common folk, and the gladiators (which are basically slaves and technically don't count in the power dynamics of Falena) regardless at least.
If he hadn't proven himself a capable leader in a time of crisis, I think he would have simply be dismissed as a foreign barbarian. Barely tolerated over his Father-in-Law, because "barbarian" or no, he was still better than a weak, ineffectual leader.
Hell, even with Ferid being well-liked in the game there's still very much that "I can't be racist I love [x] people!" vibes with many, because there's so many conversations of people shitting on foreigners and then go "Oh, no disrespect to his Majesty!" and of course the nobility and influential shitting their pants when the possibility of Ferid 2.0 could happen for Lym's sacred games.
Thankfully Ferid has the ability to shrug and laugh most things off-- a useful disposition to have as a consort in a country that doesn't fully hide the fact they they don't exactly think you're worthy of that role.
(Kar, his younger sister on the other hand, is a certified hatergirl and is petty for the both them at least. And I've no doubt Sialeeds has done her own share so sister and sister-in-law are his personal petty squad...)