There are many crash instances where a light lower vehicle will be
fatal where a higher sitting one wouldn't. But there are also
situations where a large top heavy one weighing a lot will be worse.
It all just depends on the crash situation.

Bill, your experiences are with much older vehicles and not with
modern compact tow cars. I'd much rather hit a wall, tree, ditch or
whatever in a smaller tow vehicle than in a big SUV.

As to engine cooling capacity, I've towed for thousands of miles
including in the desert in summer and up grades in NM in summer with a
Honda Accord 5 speed and have never had to even shut the AC off.

It's relative colling capacity that matters. Smaller engines just
don't need huge V-8 radiators to cool just as well. Maybe better as
they pull a lot less weight.

The crash test comparison between a Mini Cooper and an F-150 pretty
well says it all for me. I especially feel safer on tight downhill
grades in a smaller vehicle as it is easier to control. Though I
wouldn't want an SUV or Semi to fall over on top of me. That would be
bad and make me wish for the SUV in that scenario.