I think I've worked out why Morgana feels so viscerally unsatisfying to include in the party

at least to me

I'm going to compare him to his approximate counterpart in P4 here, Yukiko

so like
they are both coded as primary healers. They get the best healing skills in the game, they get the support abilities to back it up

They both get -dyne skills, they both get some unreliable secondary abilities to use against enemies that resist their primary element; in the case of Yukiko, it's Mudo skills. In the case of Morgana, it's Miracle Punch. They're very similar.

So why does Morgana feel so much weaker than Yukiko?

Yukiko, aside from the Protagonist, is competing against five other characters.

Her best offensive skill is Maragidyne, and that has parity with the other party members in Yosuke's Magarudyne/Brave Blade, Chie's God Hand/Agneyastra, Kanji's Maziodyne/Primal Force, Teddie's Mabufudyne, and Naoto's Megidolaon.
She can't keep up with the protagonist, but that's not fair, it's a persona game and she doesn't have to.

But the key point is, even though she's a healer, including her in your party isn't going to dramatically affect your damage output.

And in Golden's postgame, she even gets Blazing Petals to really ratchet up her damage output.

Yukiko's a beast.

Morgana by endgame is competing against seven other characters for party space

He has all the same tiers of abilities as Yukiko, so what gives?

Well, contrast his fellows.
Ryuji has the same skills Chie did but it's slapped on Kanji's chassis. He can take it and dish it out.
Ann has it better with a Burning Petals equivalent in Blazing Hell. She's the mage, she deserves it.

Yusuke is a fucking monster with Brave Blade and Vorpal Blade, plus Mabufudyne, Makoto's an all-rounder but she still has a tier above -dyne skills with Atomic Flare. Haru only has -dyne skills but her skillset is so broad that she can make do without better, plus she has One Shot Kill, the -karn skills, some support skills, and gun boost/amp

If we're in Royal's postgame, then Akechi has Levaeteinn and Eigaon but also Megidolaon, Riot Gun, and some support with Debilitate. Sumire's even better with tons of crits, Kougaon, and great physical damage.

The third awakening skills range from Fantastic (Ann/Ryuji) to Pretty Good (Akechi/Sumire/Yusuke) to Situationally Useful (Haru/Makoto) to...

Miracle Rush.

Miracle Rush doesn't capitalize on any of Morgana's strengths other than his high luck, but that just involves trusting your fate to RNGesus and that's not ever going to work out in your favor because like
Miracle Rush barely does any damage
Wind also doesn't Technical off of anything really useful

as opposed to Psychic, which Technicals off of fucking everything.

Thus making Haru even better.

Sure, he's got the best healing in the game, but healing is literally the least efficient thing you can do
you only heal when your choices are 'heal or die'.

Also the return on Salvation vs Mediarahan just... isn't great
There aren't a lot of situations where you'd be healing the entire party of large amounts of health and status ailments

so Morgana doesn't have much to contribute outside of emergencies, and even then, strong possibility you won't need him because Futaba just, y'know, exists

Morgana's competing against an all-star team of ass-kickers and he just doesn't feel like he has anything to measure up.

i want to like him i really do but like

gestures vaguely at this

and the okumura thing

technically i agree with most of this, but also: his usefulness as a character in-game reflects his anxieties about being useful in-character, and i appreciate that gameplay/story resonance. morgana exists to drive plot and conflict. he does good at what he's there for.

Anxieties don't have to be rooted in reality. They're frequently irrational, honestly- and playing it this way feels... wrong to me
like this is supposed to be a team, and there's one person here who very much is behind the others
It'd be really nice, actually, if he got some extra toys over the course of the plot to really help with that

It doesn't help that for the vast majority of circumstances, P5 and especially Royal rewards well-strategized offense more than anything else
The whole 1-More system along with baton pass means that your ideal combat is one that doesn't allow your enemies to get a turn in. And Morgana has no real means of keeping up on that front.

Against bosses, his usefulness as a healer increases, but many of them just can't be knocked down so miracle X is useless, and his wind stuff just can't compete in endgame, especially since the only character he really synergizes with is ann

sumire to an extent, but again that's relying on rngesus with the crit fishing

contrast makoto who also has mediarahan and fits easily into any party with ann/ryuji/yusuke and also the elemental gun camos

or haru, who can do literally anything

Akechi has less synergy than Morgana, but also he has similar levels of 'do-anything' to Haru, though focused a lot more offensively

it'd feel better in my mind if his renewed self-confidence coincided with an actual increase in effectiveness

yeah its nice that hes anxious and all that but this is an rpg and we need fighters to handle atlus boss bullshit. put the anxiety anywhere else but keep it the fuck out of gameplay if thats what they're going for. if a character doesn't cut the mustard in battle, they get benched.

if his uselessness is the point then nobody will use him and itsca waste to equip him or even level him. like why bother.

at least magikarp rewards your patience with ya boy gyarados. that's how you do that kinda thing.