That is only if you are using the same 24-105 lens for dslr and mirrorless. If you look at my comparison, I use the EF-M 18-150 versus the EF-S 18-135. The real advantage of the M5 is the versatility. If you use the EF-M 18-150 or the EF-M 22, you will have a much more portable "camera package" while at the same time providing you the option of using your L lenses. In fact, if you look at my post in another thread, I took a pic of my son with the 50 1.2L and the 22.
Yep, I am all on board with you. If - big if - you use the native lenses for the Canon mirrorless.
I think it's more likely that we SL-1 owners who are possibly considering the M5 might own the 18-135 (either the STM or the newer USM) so here's that comparison: