A lot of very valid points thus far....
I’ve owned a 990 Adv, 1090R and now 790R and have ridden them all mostly offroad.
The 1x90 does become a handful in slow technical stuff even though my 1090 was lighter than my 990 by a kg or two if I recall. Both the 790 and 1090 make a 990 feel like an old tractor with bad brakes. That’s just a fact.
I still rate the 990 for obvious reasons, but apart from financial considerations (and looks

) I cannot see any reason not to upgrade to the 790. It is just next level!
If you’re into open gravel touring any of the 1x90s will be better bike to own than the other two.