>A rangefinder is a higher quality camera than an SLR ever was

This does not mean anything at all. The comparison is total nonsense.

>and a full frame mirrorless probably has better quality than a DSLR

No. DSLR and Mirrorless camera differ how the viewfinder works. Generally Mirrorless cameras are newer, but ranking them for quality is totally nonsensical. This is independent of the size of the sensor.

>A medium format camera can be better than all of those.

You are comparing totally different things. A full frame Camera can be Mirrorless or a DSLR. There is no comparison to be made here. You are totally confused about technology and terminology.