Is it a problem that PEX emerging from the walls is floppy
You need a pex stub-out bracket that attaches to the studs:



And a 90 pex support that attaches to the bracket:



It would be nice to have a sleeve and a escutcheon:



Your PEX will still be a little wobbly, but connecting it directly to the toilet valve is considered by many to a better solution than using a copper stub-out, because there is no fitting behind the wall.  Anyway, PEX is pretty tough.