Don't believe everything you read. It was just one guy'e experience. Conventional wisdom is the opposite, although with an SLR technique plays such a big role.
I've put lots of film through an SL and both 50 Summicrons. Like many, I prefer the optics of the 2nd version, but those earlier version feel like they're built out of rock. Both are good, and I just happen always to use UV filters.
Although the real magic with the SL comes with a 90mm lens. Those microprisms just pop!