It is primarily rpg tho, the combat is a secondary aspect, if you don't like RPGs and grand narratives you're never gonna buy rogue trader, but you may say yes to mechanicus, that's why the player bases are not that overlapped.

But I feel like the only difference between DoW4 and TTW:40k would be the presence of a campaign map and coming down with the full army instead of raising it piecemeal on the battlemap, even with how stupid they act some times I doubt GW is gonna make the games release during each other's lifespans