Didn't they say at one point after gt5/gt6, that the campaign started to feel the same or not as interesting , and they started hyping forza campaigns and need for speed shift as the way to go? Maybe i'm wrong, maybe it was one game that had a mediocre campaign. I myself haven't haven't played forza or shift, but will campaign that gt fans are used still feel fresh, can it compete with forza or shift? In terms of feeling rewarding through progression, which is what shift got rave reviews for.
As for forza 8, I saw the trailer and wasn't too impressed visually. The textutres and vehichles did not look as good as in gt7, or sport. Maybe it's the art style but it doesn't look photo realistic. I honestly can't see it topping gt7 in the visual department. PD put too much care in cars and track design.
Way too early to say which actually looks better. There is barely any FM footage to make a comparison.
Going by the past, gt has always gone for more photo realism, and with the gt sport engine tech made to be future proof and taken advantage of future hardware, I don't see that trend changing. I was looking at the forza 8 trailer, even though work in progress, it looked to follow the style of forza 7. What I noticed was cars and track detail not as great as gt.