The internet towing police will be here soon. When they arrive I suggest just grabbing a beer (or what ever your beverage of choice is) and listen to them all. Though I will likely disagree with many of things said, they will likely be speaking the truth - on both sides of the argument.
The little bit that I believe to be true:
I believe there is exemptions for RV's - this is why a 90 year old 90 pound, little old guy can jump in his tandem axle diesel pusher $500,000+ motorhome and cruise the country with out a CDL. I'm not sure if there are any RV limitations but some of the big motorhomes have GVW's in to the 40,000's, possibly more
I believe if you physically weight more than 26,000 you need a CDL - unless its an RV
F250 - GVW 10,000 can tow up to a 16,000# non-RV trailer without a CDL Once the truck GVW sticker Plus the trailer GVW sticker adds up to more than 26,000# a CDL is required - Unless it's an RV
F350 - GVW 11,500 can tow up to 14,500# non-RV trailer without a CDL Once the truck GVW sticker Plus the trailer GVW sticker adds up to more than 26,000# a CDL is required - Unless it's an RV
F550 - GVW 19,500 can tow up to a 10,000# non RV trailer without a CDL. I'm not sure if there is an RV exemption here.
F750 - GVW 25,999 can tow up to a 10,000# non RV trailer without a CDL. I'm not sure if there is an RV exemption here.
With the big trucks in a non-RV situation I think you can still physically only weigh a max 26,000# without a CDL
These trucks (F250/350) don't have the GCWR listed on the door sticker so I don't think you would get a ticket for being outside what the Ford towing guide says is allowable. However the towing guide would likely become an "Exhibit" in a court case should you get in an accident...
The towing guide - in my opinion - is a waste of a piece of paper. It says a 2021 F350 (non Tremor) can conventional tow 20,000# yet an F550 can only tow 18,500# even though the F550 is MUCH more capable. The towing guide is clearly not a recommendation of the actual capabilities of the trucks.
I do a good bit of construction work so I want the most options in towing and I will likely just get a CDL and be done with it, since i have a F350 ordered. And we have a F550 and a GMC8500
If your use case is to primarily to tow around your RV, a 250 Tremor and a 350 Tremor can essentially tow the same thing however the 250 will run out of cargo/tongue/pin weight 1,500# sooner than a 350. If you want to tow a utility trailer with a GVW over 14,500 you're probably better off getting the 250 and dealing with limited payload capacity (knowing that this limitation is only on paper - they can physically carry same; they are the same truck)
There is also some extent of reciprocity between states. this gets very complicated with big trucks but I believe on class 3 and under our home states rules follow you around - this could be wrong and if any one knows more on this subject I'd like to hear
These are my thoughts. I'm sure I'll be corrected and I welcome the criticism!