Indeed, a 3,500# tow rating doesn't necessarily mean you can just connect the latch the coupler of the 3,500# trailer onto the ball and go. Most of these TVs lack prewiring for electric brakes and most have a fairly wimpy ATF cooler built into the standard radiator.
But it doesn't take an ASE certification to figure out how to custom wire a brake controller and install an aux air/oil ATF cooler. Then again, most snowflakes out there these days call for help when they get a flat tire. Maybe I am expecting too much.
Our 3,500# rated minivan needed all those things and has no real trouble pulling 7,800# GCVW (rated 8,265# max). Sure, it needs to pull grades in D3 instead of D5, but that's not "struggling," it's typical towing behavior.
Maybe that's why we're not seeing more of these creative combinations out there. People just can't do anything that's not "plug and play" anymore.