I went from the E-PL5 to the E-M10 then to the E-M10 iiUnsure to get the M10iii or M5ii though.
The step from each was significant. I really liked having a viewfinder and the stabilisation on the 10ii was better.
When the E-M10iii came out I struggled to see anything that was better and some things were worse.
The big one related to dropping Bracketing and HDR in P/A/S modes if I remember.
Unless you want 4K video then the M10ii is as good.
I played with the M5 line and it's not much bigger than the M10 line - but I never take my camera anywhere where weather sealing is needed.