“Through toil at both of them” seems to be the pashut pshat in the mishna. (Artscroll writes it without citing anyone.)
Also, I realize that those who opposed the Mussar movement did not do so due to an aversion to good midos. Considering “yigias,” if it’s referring to derech eretz, it’s referring to studying derech eretz, no?
Noch amol?
No. We don’t darshen mishnayos by ourselves. Especially when it is a mishna that has numerous rishonim which explain it.