As a happy owner of FFXIV on Steam, I'm slightly annoyed by the lack of proper Steam client and account integration that this release of the game has.
Installing the game through Steam should distribute the entire game through Steam, not just the launcher that I then have to open in order to download the actual game client. More importantly, there shouldn't be a need for an additional launcher and pressing play should take me straight into the game much like it does for other online games such as Destiny 2.
I don't mind having the Square Enix account for tracking my progress and being able to make that cross-platform for the macOS and PlayStation versions of FFXIV also but beyond that, Steam should be my point of interaction. Adding, changing or cancelling a subscription should be possible directly via Steam rather than going onto Mogstation and billing through Steam.
Likewise, purchasing optional items from the cash store should also be a possibility directly via Steam. As a customer, I'd much rather billing through Steam (or PlayStation for that matter) than doing subscription/cash shop through a separate store. It's one less company that's storing/processing my billing information directly so it's a lesser security hassle.
As a happy Steam customer, one that's also looking at buying a Steam Deck, I'd love for the Steam release of FFXIV to actually be a proper Steam release and not a standalone game poorly thrown onto the platform as it currently is. Many big publishers are already releasing like this on Steam, FFXIV should be another such release.
(I'm not about to get pedantic about account security as nothing is truly hack proof but PlayStation/Steam has a really robust system and I've personally never had any issues keeping an account safe that way. I'm also aware that platforms can targeted directly via malicious attacks but I'd trust a major platform holder more than an individual publisher, especially one such as SE with a janky store front as it is).