Just a question how many balls are you trying to juggle at the same time?

Now onto your query, I think to some extent the market for such games are saturated (but ofc hungry for a good new title, any market in this climate of globohomo is :D)

Also you are mixing a lot of genres that goes more or less hardcore when it comes to grand strategy (the mention games are Paradox interactive, presume Stellaris,hoi4, etc and CA (total war series) and then Age of Wonders 4?) where some are true to the genre and others are more classic 4x.

So with that in mind I've been wondering about the type of grand strategy game people would want that doesn't have the DLC garbage spammed everywhere. I would personally want something that takes over the Total war series and does the overview and battlemap well, and I would like a medieval period perhaps the up till the late medieval since that gives your overview map a lot of fun with different ruling systems which could give flair to different factions and it also can ensure different specialties of units while keeping it somewhat grounded. The major point except fixin AI in battlemaps is the need for opponents to follow personality trait more than just being random retards that they usually are. I'm not against giving the ai cheats on higher difficulties levels but the core need to be somewhat thinking to provide more of personality that makes sense in the context. Also, I want naval battles back.

Sort of like the anime GATE but in the reverse and I'd have it where Rome ends up invading a fantasy world which would be hilarious I think but also somewhat interesting.

What level of tech would this magic society be? I presume the romans would be the underdog requiring to reverse engineer the magic from this new world? Or would it awaken Romulus? I'm not really seeing the appeal of this theme tbh.

I do know that Age of Wonders exists, don't get me wrong but boy did that game need to be optimised, don't know if they've fixed the issues yet.

Depends on what optimization you are talking about, to some extent it is better now. Altough that could be that they nerfed the reserch rate since to some extent the slowdown was tied to the amount of research (how?! I do not know, but like all things the engine programmer is most likely alone trying to keep something working) which has been nerfed. Still got the horror of huge log files being created in which I do not know how to turn of logging weird telemetry and dumping it as logs. which can be quite large after a game. And don't get me started on how AoW4 increase the amount of globo homo by taking a series name and just trying to turn it into a blob.

On entirely unrelated thing, have you seen this old comments of Total war series being mods on top of mods xD