Endwar did this pretty well, from memory. You could have a 'front', and then have individual battles on that front (that would be well below the level of HoI battles, although in HoI4 you could have WT-scale air combat), and then the outcome of those battles feeds into a larger map. I like your idea of going about it the other way, by adding a tactical layer to War Thunder. Not saying it couldn't be done of course, but it'd be a lot of work (particularly to do right) with relatively little payoff.
For a start, there's no way known that anyone playing in a battle would have any significant impact on the outcome, and you'd be building a game engine to simulate battles of up to tens of thousands of individuals and hundreds of tanks and aircraft on each side, for the benefit of one person being able to drop in, in their plane or tank, and get in amongst it. alan aztec - War thunder (slav thunder) (2021) uamee ft. X-Com and Total War battles are still much smaller than HoI-level battles though, and having tactical layers to strategic games is a bit different to having 'you're an individual in a battle' layers to a strategic game. Life of Boris - No Ruski Pop (2021) uamee - how to cook pelmeni (2021) uamee - 1911 v tokarev (2021) uamee ft.
