My (European) knowledge of cars and towing limits is a bit rusty, but for what it’s worth:

The auto company I worked for had a European tow limitation that required pulling up a 12 percent (IIRC) hill. I think it was a company standard rather than a legal requirement.

I had no direct experience of USA practice re towing limits, but in other contexts (engine performance when not towing) there was mention of American vehicles having to perform on Pikes Peak, a well known USA mountain? It may be that sort of expectation that led to lower towing limits in the USA for European vehicles – or as suggested above, it may just be caution re legal liabilities.

Another thing – not only is wheelbase a significant factor, so is rear overhang. A short wheelbase car with a long overhanging boot (Europe)/trunk (USA) is a bad combination, and leads to a low maximum stable speed above which anti-snaking has to be used – either the driver’s skill, or an anti-snake device. The latter are commonly available in Europe.

I leave to others to recommend what is best for towing in the USA, but I suspect that what we can get away with in Europe is not suitable for at least mountainous areas of the USA.

Chris N.