Joe is talking about these martial arts as systems, and as systems they are bottom of the barrel, and barely existent in MMA. When you see a so-called Karate, or TKD guys doing well in striking it's because they are performing standard kickboxing tactics, which have always been relevant.
TKD, and Karate as stand alone systems are pretty useless, and that has been proven time, and time again.
Look, it was cool that your parents enrolled you in a Karate, or TKD class because you wanted to be a Ninja Turtle. It's better than eating Cheetos, and watching cartoons, but neither of these arts alone will make you a competent striker. There have been few successful adherents of either art in MMA, and that's pretty significant, considering the prevalence of Karate, and TKD schools across the globe.
We already know what the favored styles are in MMA, and we've known that for quite some time. Karate, and TKD are not it. You're better off joining a kickboxing, or boxing class.