Actually both break immersion. No z-axis break it and irrealistic jump break it too.
Jump to go on something? No, normally if the place you want to get to is low enough you'll just step on it and if it's too high you'll climb, not jump. When going somewhere you would walk or run and in front of an unsurmountable obstacle you would go around it, not try a series of well placed jump to go over it.
The only time were jumping help immersion is to get jump off sometime or to use it to cross a gap.
I think i said it already in this thread but
for a jump that help immersion it would need to be realistic meaning not jumping to high, not being able to fall from too high(at least not without dieing) and not being able to move around by jumping as fast as by running.