I don't know if it qualifies as mythical but having used lenses from Canon, Nikon, Leica R, Zeiss, Sigma, Tamron and a few other M42 lenses I'd say that each brand and within each brand certain lenses have their own special look. No lens is perfect and besides perfection is overrated!
If I was to compare 50s (and I mean 50mm leaving other lenses nearby like 40, 55 and 58mm out) I have tried these:
Canon 50/1.8
Nikon 50/1.8D, 50/1.8G, 50/1.4D
Olympus OM 50/1.8
Leica Summicron-R 50
Zeiss ZF2 50/1.4
Some dinky old M42 50/2 lens.
Of those they all had their own look. Least liked, the Nikon 50/1.8 (D and G) were really bland and low contrast, just about acceptably sharp wide open and basically a waste of money, IMHO. The OM 50/1.8 was super sharp and contrasty but otherwise a bit indifferent but probably the best value of them all (got it for £29 complete with OM-1MD body). The Zeiss 50/1.4 was the most "flawed", ie focus shift, soft wide open (in a pixel peeper way) but it was my favourite lens across all 135 systems I've tried. Until I got the Summicron-R, which is, again, a flawed lens in some respects (not that sharp wide open) but it is now my favourite and the reason I bought an R8.
So mythical? I would think mythical is something that is so perfect it is beyond perfect. But I don't think they make such a lens. I mean if you believe the internets a mythical 50 is probably the Zeiss 50/2 MP but I've gone way past that "sharpness at 400% in photoshop with contrast that makes your eye hurt" stage.