Every bashes TKD because it is rubbish for the time spent in it. I also out kick people and came in to mma a step up than other newbies (as SWldn said) but for 5 years training i should have been miles ahead. Its not that im shit at it (black belt, won numerous competitions) its just not that great for mma. I've been doing mma 2-3 months and use a lot of teeps, leg kicks and can high kick and do reasonably well against people who have trained nothing but i would still rather take it to the mat against anyone with a reasonable amount of training in say Muay Thai. I feel TKD teaches you bad habits for mma, the point stop nature of sparring mean you go for speed not power, it also means you are less conditioned to think about defence than someone from another stand-up discipline as you only worry about the first strike. I often spar and get a quick kick or combo in, only to find i get tagged in the head with a right hand because ive been conditioned to think only about getting the first hit in not to worry about what happens after that.
Overall i would say TKD has helped me with MMA, due to my flexability, ability to use kicks, reflexes etc. i just dont think its worth the time commitment. I think i would have been a lot better if i had say used those years to study Muay Thai or boxing, which are more adaptible, and in my opinion more useful in MMA than TKD