I think a lot of discrediting the old school martial arts has to do with the "tough guy" mentality, these young guys (the main demographic who derride the traditional arts) has to do with the fact that these guys feel the need for everyone to think they are naturally tough, and they want everyone, themselves included, to believe that they are so naturally tough that they could beat a martial artist in a fight.
That said, a lot of pure martial artists would lose to these "tough guys" in MMA fights, since most martial artists dont train wrestling, and can often be Lay n Prayed. That said, you can Lay and pray and win the contest, but you can still losr the fight imo.
That said, I still dont believe, no matter what Taekwondo practicioners say, that TKD has much practical application in a real life combat situation. It looks fantastic, and its obviously very good for flexibility, but the techniques just arent useful or practical. Furthermore, things like Dim-mak and the one inch punch just dont sway me. I won't be fooled by myths and legends. However, things like Karate, and some chinese arts, are, despite what many MMA fans say, effective striking systems. So yeah, they aren't Muay Thai, but thats just how she goes!
One thing I would love to see though, all these guys who say that Karate is crap etc, mostly internet warriors / high school wrestlers turned "MMA" fighters, fight Feitosa or Hug if he were still alive. Even under wrestling biased MMA rules, 99.9% of them would still go away crying or unconscious. And then post on Sherdog about how the ref distracted them or something.