Thanks for the well thought-out reply and apologies for only coming back to you the next day but I was too tired to answer this properly at 2 am my time!
With regards to your first point, I completely agree - it's a shame when a dev gets sidetracked a lot by gameplay/combat improvements to the detriment of advancing the plot/making new art, and given that I've heard earlier in this thread that version 8.0 might require a full restart and won't support previous saves anymore, it's also a major inconvenience. (especially as it's not the first time when the old saves were rendered obsolete for this game...) Fighting droves of undead just to level up also added plenty of extra grind to the way the game works, and I truly hope dek will not end up abandoning the project cause it got out of hand or handing out short (in terms of gameplay time/story) delayed updates for years until he completes it!
That said, there could be many reasons he focused on revamping the gameplay and combat mechanics the way he did - it could be he had writer's block and decided to focus on other ways to improve the game (as the class system, all the weapons, skills and perks do make it a more polished and better experience gameplaywise) for example, and if that is the case he may return to more frequent plot-driven updates eventually! I know as of late he's mostly just promised updates and not delvered, but here's to hoping at least! Obviously you could also be right and he might've gotten bogged down in too many perks, skills, systems and buffs he has to think about for the future dominas as opposed to the plot or the various post-enslavement scenes for the existing Dominas, but by this point I'm mostly hoping that's not the case or that he managed to sort most things out during this long break.
Domina is a good game and I echo your sentiment that it would be terrible for this to go the way of "Under the Witch" and over-complicate itself to desruction, (which is possible) but I still have hope in dek eventually picking himself up and finishing this game! (maybe it's a misguided hope because I'm not his supporter/haven't checked his patreon too often, but he should see people are mad about his delays and perhaps that'll have a positive effect)
It's also nice to hear Salia Coel did that - I haven't checked Femdom University in a while so I should probably take a look at the latest updates! (really hoping for new Skullgirls content) As I said, thanks a lot for the nuanced answer and let's hope your worst predictions won't come to pass!
(although, especially if you used to be a supporter, you have many reasons to be frustrated with him...)