My M6 Classic has the 0.85 finder as do my M7's.
Yes, the M6 does flare, whiteout or whatever you want to call it in certain situations but it certainly doesn't make the camera unusable and I continue taking pictures preferring to focus on the job at hand. All photography equipment has faults, quirks or however you want to refer to it and one learns how to deal with those items. If you obsess over small problems than you can't get the job done.
Maybe my perspective is different having worked as newspaper photographer. If I told the City Editor that I was having problems getting a shot he wanted because of flare/whiteout, he would have thrown me out of the News Room!
BTW, I have had a single stroke M3 for many years. Yes the finder is nice but I never use the M3 anymore, the M6 and certainly the M7's are much faster cameras to use with the buit in metering and the ability to use the Motor M's as I do.
My rig is usually two M7's with Motor M's and the only thing I have to do is focus.-Dick