I like it when "streetfighters" claim that they don't need to train for endurance because their fights only last a few seconds. The funniest part is that most "streetfighters" have only been in one or two fights and wouldn't know shit about getting in shape anyhow. Legitimate streetfighters tend to know better, albeit not much.
You need to build up your endurance even if all you train for is a sudden, unoprovoked self-defense situation that's probably never even going to happen.
Skill training definitely feels better when you're fresh. It's also a lot easier. Easy is for wimps. If all you're interested in is pretty looking poomse or fancy looking tricks that might be fine. But when some asshole like me shoves you off of your stool in front of the girl you were hopelessly trying to mack you're going to be just some other joke who traditional martial arts training didn't work for. You'll join an MMA gym and hang out with the other prettyboys who've been bullied and preach online about the superiority of MMA over the older self-defense systems. Well no shit, retard. Competitive mixed martial arts fighters train for endurance. They're not going to panic when the adrenaline dumps because they feel it dump all the time.
It doesn't hurt that competitive fighters (boxing, wrestling, judo, MMA, etc) aren't going to be shocked at the prospect of physical contact either but that's somewhat of another matter. If you really wanted to learn how to fight you would train in a gym with fighters who actually fight. But not everybody does and they've all got their reasons so in the meantime stop bullshitting and just do your cardio work like everybody else.