I don't think it'd be particularly worth Capcom's resources to make major changes to the game's content or gameplay, but yeah, it really should've been Genma Onimusha. I still bought it, played through once, realized I absolutely didn't care to deal with finding all of the hidden Fluorite, let alone doing the atrocious Oni Spirits minigame again, and set it down.
I think - beyond remastering Genma Onimusha instead of Onimusha: Warlords - it also would've been a good idea to unlock Ultimate Mode (infinite magic, start with the Bishamon Sword) as a reward for beating Hard Difficulty, not as a reward for completing an utterly terrible minigame. That's how Onimusha 2 did it and it really felt best in that game. That, or some kind of straightforward new game plus, would have felt best and would not have required a ton of additional work on the part of the developers.
I'm definitely hoping that Onimusha 2 - if it's ever remastered - adds some kind of New Game Plus mode - all of the branching storylines (and the inability to unlock every single upgrade on a single playthrough) are really suited to it. Give me an excuse to play through a bunch of times, unlock all of the top tier equipment for every supporting character, max out everybody's HP and MP bars, unlock every single Necklace, et cetera. Keep the Rekka-Ken unlock behind beating Hard difficulty, that's fine with me. The missable content and gift-giving minigame stuff is definitely Onimusha 2's biggest flaw, and doing a better job of encouraging multiple playthroughs would be a great way to remedy that.
Dawn of dream has the best combat and is packed with content.
Ehhh... it's got the biggest total moveset but that doesn't mean it's got the best combat. The game is way too much about grinding higher stats/stronger equipment and not enough about your skill in combat; the fact that it's more of an ARPG than an action game automatically downgrades how good the combat can be imo. Not to mention that - in practice - the ACTUAL combat is just doing the magic chain issen move over and over again against literally everything in the game because it's easier and more overpowered than literally anything else you can do.
Definitely agree that it's got tons of content, though. I enjoy the way that different characters can unlock different paths and that you're encouraged to revisit older areas of the game to unlock previously unreachable treasure.