You're not playing against good auto users then. Any auto user taking on the M79 within its range is stupid. Staying afar, the auto will always have the upper hand. That goes for pretty much every mid to long range weapon -- a M79 user should be dead before it's even in range.
I also don't see how you can "spam" the M79 shot when it only shoots one every three or so seconds. If you mean just lobbing shots down on spawn or high traffic locations such as on ctf_ash, then, sure, kills can come easy in those specific situations. No different than raining granades on the enemy -- it's hardly a skilled tactic.
It's easy to dodge auto shots from long-range too, you just have to be careful while you're doing it (as generally, they're running as they spray... so if you're trying to find spots that the bullets are missing, you have to concentrate at the same time on everything in front of you). Essentially, I've gotten good in Soldat at ducking and running in, so alot of the time I CAN get in range with an auto user because they don't see me in time (I mostly play realistic).
And when I said spam, I actually meant I ONLY used the M79, not that I lobbed nades everywhere from it
Randomly firing M79 shots comes only in crowded maps for me, where I know I'll get some kills. You're right, there's no skill there at all. I was just saying I used to ONLY use the M79, now I use every other weapon too.