I use an ExpeditionMAX to tow my 7000 pound boat. It does a much better job towing than the YukonXL Denali it replaced, but still not nearly as good as my RAM, but that really isn’t a fair comparison.
Stability with the Ex is fine. Power is really really good. The only issue I have is that it gets very hot (engine and tranny) towing I70 through the mountains in Colorado. If I were towing all the time in the mountains I’d be worried, but very few people do that.
Given those two choices, I’d go with the Expedition hands down. Huge advantage there is the engine - personally I’d never tow that much weight with a 5.3, and last I checked you can’t get the 6.2 except in the upper trim levels. That said, the 3.0 in a Tahoe would be intriguing.
As far as “tail wagging the dog” on a long trailer, I believe all modern tow vehicles use the trailer brakes to eliminate sway. I know I’ve never felt it with my boat.