It helps for me that the dungeons in P4 are directly involved in the development/introductions of new party members, whereas in P5 some of the dungeon owners can feel a little bit underdeveloped. I think describing my issues with P5 would take a while, though in brief I guess one element I can mention somewhat safely is that I feel there were some rehashed elements from Persona 4 that didn't need rehashing or that P4 did better, but that's just me.

I think in terms of individual character stories it also comes down to personal preference. (I mean, all media appreciation is, but here even more so than usual) I think Kawakami for example is almost universally liked, (by me included) but I think there's plenty of people who like Iwai and Hifumi too. Hell, there's people who wanted Hifumi to be a part of the Phantom Thieves because originally she was designed as a playable character according to some official documentation. I'd debate with people over the merits of the overarching story, but probably not the optional, individual stories. I think the beauty of Persona is that you don't necessarily have to force yourself to hang out with a character you don't like.

In my experience I'd say I've liked and disliked an equal amount of the various confidants and social links across all the games... the writing for them follows a lot of the same formulas structurally, and I don't think they've significantly improved or gotten worse since Persona 3. That's a pretty bold claim to make- I'd have to go through all of them again and take a serious critical look at them for me to be able to make that claim in good faith. That would take forever, though...

I'd have to check the Phantom Thieves percentages though, I never used it in my playthrough because I didn't want to be put under peer-pressure.

I can totally see why you would prefer Persona 5 though, and in many, many ways P5 blows the rest of the series out of the water. Even just the aesthetic alone counts for a lot I think... I just think the last 20 or so hours of the game could have used a quick script rewrite or proof-read. And the ending is paramount, after all.