I recall the time when, as a proud Nikon F2 owner, I bought a used Leica M5 with 4 lenses, dirt cheap!
Then, after a vacation in France, I checked the Kodachromes (yes, I'm that old!).
Next day, I went to the local dealer, sold the F 2 (Greatest SLR ever), all my Nikkors, to buy a Leicaflex SL
with 28, 50 and Apo 180mm.Later on came lenses from 21 to 560 mm...M and R.
The Nikon lenses had no chance compared to the Summicrons, Summilux, Elmarits & co., with the exception of the R 28 mm, which is quite weak.
Also, mechanically speaking, the Nikkors WERE poorly made, in comparison.
In the meantime, Japanese lensmakers have tremendously improved the quality of their production, and yet...
As to Leica, the later SLRs (R 4, R 5 etc...) lagged behind the Canons and Nikons in features and quality.
But the lenses are still a world apart, and the M remains a wonderful camera.
I'd suggest that before bashing the Monochrome for instance, you enter a Leica store to play with it for a few minutes, the change your mind, and rob the next bank!