Too bad that in colder climates where it's exposed to the cold, such as a
seasonal cabin, the PEX gets brittle after a few winters and starts cracking
and splitting randomly, usually behind the most difficult to get at wall

I havent seen this, PEX appears to expand and contract better than
copper.

Where copper will split PEX just gives a little.

Although it shouldnt be left to freeeze for years, without
winterizing.

Do you blow out lines and fill with RV antifreeze, the non toxic type?