Jab, cross, staight, hook, uppercut, elbows, knees, roundhouse, sidekick, front kick... Pretty sure those are TKD basics and they seem to be pretty common in MMA.
Gracie Jiu-Jitsu may be minimal, simple, and effective but that's not enough if the fight doesn't go to the ground. GJJ is not the MMA solution any more than any other style of martial art.
I'm tired of people not understanding there is a functional side to TKD and an artistic side. TKD is a martial art and any martial art requires adjustments to be an effictive fighting method.
I am not sure about your experience with TKD, but I went to a lot of different schools in my area and my experience was always the same.
I spent a lot of time doing Muay-Thai before I started going to TKD gyms so I was a pretty descent boxer. Just about every class I went too I would use good technique on jabs, crosses, uppercuts, hooks, etc...I would always get corrected and told "this is how we do it in TKD". It was always less effecient and flashier ways of doing it IMO.
Another thing I would get corrected on quite often was I love kicking the legs. Every class I went too I was told immediately "no leg kicks". How are you going to learn how to defend or use leg kicks when you don't use them??
Several of the schools I went too (not all of them) taught to roundhouse kick with the foot and not the shin. Some had adapted using the shin; although I'm not sure which is more traditional. To me kicking with the foot is stupid...what happens when you break your foot? Then you are in the middle of a fight and can't stand.
Most of the schools as well did not allow strikes to the face. Same as leg kicks...how are you going to learn how to defend or strike to the face if you can't do it training? You can't.
From what I saw of the stances, most of them were pretty useless. To me the stances were set up more for point sparring and not street fighting. Some big leg stance isn't going to win fights on the street or against kickboxers. If you don't believe that just take a look at Machida and how he got his leg kicked to death last week.
Kata was the all time worse thing I saw. I did Karate (got a black belt in Shorin-Ryu Karate) and I never agreed with kata. Some people say it's useful for something...what I don't know. This isn't the Karate Kid, nobody is gonna stand there in awe while you do some stupid form...you are gonna start doing it and they are gonna kick the crap out of you.
My biggest gripe with Karate and TKD is the belt test and the fact that they give belts out for money. When I got my black belt I paid about $1500 to get it. I have seen schools that charge more than that. When I got my belts in BJJ I paid nothing, I went into class one day and they handed me a belt and told me "you earned this".