As far as Marvel's situation, they haven't ever really done a "reboot".
That's completely inaccurate. At the beginning of Secret Wars last year, the Marvel Multiverse was destroyed. Dr. Doom cobbled together a kingdom, saving (or recreating) everyone he could. A handful of heroes who survived the destruction in lifeboats orchestrated a civil war against Doom and won. In the end, the new unified universe was created by Franklin Richards. It combined elements of the traditional Marvel universe, Ultimate universe, and the cinematic universe.
It was a full-scale reboot.