M5 owners, (and 18-150 ones) please chime in.

It's probably the DIGIC7 itself has a different bias, hence it's more extreme.

I concur, although upping the exposure comp appears to be the only viable solution aside from bumping exposure on RAWs in post which is a pain, the former is a "hammer" that can produce "correct" (to taste) exposure in some circumstances, and way too much in others, it's akin to my problem with Picture Styles, I'm using a custom one that gets it "right" 90% of the time, and the other 10%, I'm left with overblown oranges as I don't like the default color bias of the M3/M5 any more than you like the exposure bias of the M5. The RAW exposure bump, sure, works, but royal pain in the neck as that's lots of review and adjustment IE time, ditto with my color style issue. I ultimately settled on having images right 90% of the time and applied my custom picture style, which I might recommend you do the same, just bump your exp comp by +1/3, may not be the full 1/2 you want, but it'll get you closer without overblown chance at +2/3, just my two cents.

Your only other alternatives are stick with the M3, or even consider a G1X II. The latter is infamous for highlight blowouts though, in my book, drove me bats, but otherwise it's a good performer.

After chomping on it (and my breakfast) maybe try an exposure comp of +1/3 and use a DPP4 recipe (or LR batch) with another +1/8 exp comp on your RAWs (if you're a RAW shooter). That should give you darn close to 1/2, but at some minor noise expense as exp comp of +1/3 on the camera results in either shutter/f-stop drop or ISO push, vs RAW pushes result in ISO bump only. Although somewhat clunky, a 1/3 camera bump and 1/8 RAW post batch is a pretty close solution for your needs. I might just try 1/3 push on the camera for a while though first and shoot RAW, and play with the RAWs if you it behooves you.