A lot of the critiques you’ve outlined about the combat design are things I can agree with but I wouldn’t quite say that I find the Penitent One to be feel weak. Maybe I would have said so initially but definitely not now that I’m about 13 hours and most enemies die within a few hits or in a single hit with the upgraded dash attack.
Similar to you, though, I’ve also had the most fun with the combat and utilizing the various tools (Mea Culpa abilities & hearts, prayers, rosary loadouts) in the boss fights.
My favorites have occurred in the back half of the game (after opening the bronze door) and my absolute favorite one so far is an encounter that occurs at a similar scale as the Esdras fight (which I have come to appreciate less as the game goes on because there are enemies with the same moveset that appear very frequently later) that was a total surprise when I first encountered it.
The moment-to-moment combat, as you mention, doesn’t compel or demand you to utilize the full potential, or even a partial potential, of the moveset and is kinda dull as a result. I’ve been avoiding parrying (because I don’t actually like parrying against AI in games) and abstaining from using Bile Flasks by using that one Mea Culpa heart and it’s purely just something I do to get Tears and I’m almost at the point where I won’t actually need anymore Tears too…
I suppose when I said the combat felt “flimsy” earlier I was mostly referring to how, less than two hours into the game at the time, I was struggling to discern how certain properties worked in the game. Things like invincibility frames on attacks, whether or not you can dodge-through enemies or attacks, which attacks are parry-able vs blockable, how knockback affects you; I’ve got a better feel for it now but occasionally it feels like any of those things seem to arbitrarily change depending on which enemies I’m fighting or how big the platform I’m fighting on is.
That being said, I’ve probably died more during the platforming (mostly via accidentally walking into pits) than during the combat. Not that dying is a huge issue either since the only actual penalty for dying is that you have to walk back to where you died to collect your Guilt. I could see myself having such a worse time with the game if it were more punishing than it already is.