Yeah. It's like, if you had an Operation Desert Storm game, you wouldn't expect to see 40 US Marines all lined up in a block or a gun line. It wouldn't make any more sense for Space Marines or Tyranids. In a game with landspeeders and grav tanks you'd want an engine that moves a lot quicker than the Total War games.

And even aside from gun lines... diplomacy seems out of place in a 40K game. The whole politics, government, espionage, taxation, trade and religion components would make no sense. Basically everything that isn't moving armies around, and I guess assassins. It's wildly uncanonical to be recruiting and training Marines on-planet over the course of a campaign. I think you'd have to scrap 90% of the turn-based game, and then why are you making a Total War game at all?