I see them as different roles, so maybe this can help. I see 6.5G as a capable round that was designed to fit in a compact magazine. It is efficient and effective, and while it can be pressed into long range quite effectively, I don't see it as a dedicated precision round. Nor do I see AR's, even kickass ones, as a cost effective way to shoot at or beyond 1000 yards.
6.5 Creedmoor is pretty inexpensive for very high quality match ammo, and the Tikka is a sweet action. It is a serious shooter. The difference between Grendel and Creedmoor is a few hundred FPS, but that allows you the flexibility to get heavier projectiles in the 140-147 range.
Having been faced with this choice myself, I went the Tikka CTR 24. That Grendel is tempting, especially the Larue. But I'd still get the Tikka first if I did it over again.