I think that the biggest difference is that with a piston engine, a windmilling prop has to drive the whole engine against it's own compression. A windmilling fan-jet engine normally only turns the N1 section, which produces surprisingly little drag. You have to be going really fast, like above 250 KIAS, to even notice rotation on the N2 gauge.

If you have ever tried to hand prop a moderately large piston engine, you know how much effort it takes to get it to turn. You can walk up to the front of a 737 and start the engine rotating with one hand. If there is any wind, it will probably already be rotating. If there is a tailwind, it will just as easily rotate in reverse.

Joe