I think the reason why SotR ultimately fails, and TBoSaS has less opponents (except for the crowd who would lynch you for enjoying Snow's character at all) is that the latter doesn't retcon anything from the original trilogy. It doesn't even recontextualize anything. It just adds flavor to certain scenes, but - strictly in terms of the books - not much. Specifically one, the conversation between them in Catching Fire, when he mocks her for Peeta seeing through her act. Because all other scenes now being used to show parallels between TBoSaS and the trilogy are movie-exclusive, although written with Collins' help, which indicated that she might have a vague idea of Snow's background at this point. I'm not saying that she already had Lucy Gray Baird in her mind back in 2012, but surely there was some idea brewing.
Still, TBoSaS doesn't change much. It never tries to convince you that, had he not met Lucy Gray, Snow would be a nice young lad, and not a cold-blooded dictator. If you don't lack media literacy, it also never tries to reframe Katniss-Snow conflict as him holding personal grudge first and foremost. Sejanus was literally invented to show the readers that Snow will eliminate anyone, who he perceives as a threat, and Katniss is a threat to his regime. Lucy Gray's existance and her memory surely added some personal bitterness, which might add new optics to Snow's personal torment of Katniss in Catching Fire, but the entire epilogue indicates that, while LGB will always be a thorn in Snow's side, he is perfectly capable of functioning and achieving success without thinking much about her every day.
Simply speaking, TBoSaS is like ketchup to the trilogy's fries. You can eat the fries without it, and they're still delicious, but ketchup adds something without taking anything.
SotR, on the other hand, serves you carrots instead of fries, and when you start to protest, it explains to you that you actually asked for carrots, that you had to read the menu wrong, because the menu says 'carrots', and what do you mean that there's a picture of fries next to the price? It's all some sort of the great potato propaganda. You were wrong for wanting fries. It was always a carrot, so eat it and shut up.
