The 3500 lbs would have to be dry weight for a 22.5' TT and also because he wouldn't have run it through a scale yet. We used to tow a 20' TT that was 5K lbs fully loaded with an F150, but the TT would have been a bit heavier due to being dual axle. We had a basic Husky round bar WDH and it worked fine but was a bit of a challenge sometimes in strong winds and on interstates with semis going past. I wouldn't have towed it without a WDH.
Don't know about the newer F150s, but a receiver without a WDH is typically rated for 500 lbs max. OP's new TT could have a tongue weight of 600+ lbs. No fancy dancy $800+ WDH needed but I would go for a simple round bar one. If sway seems to be an issue, could always add a friction bar.
Note that if you do find you have a sway issue, there are other contributing factors like tire pressure in TT & TV, and having the trailer level to slightly nose down.
