As @
BehindBlueI's stated, retention is more skill and software based, and while having some kind of retention aid built it to the holster is nice (one reason part of me still likes leather holsters - even though I never wear any for the most part), it is not the end all be all.
The true problem with the clipdraw has little to do with on belt retention. The issue is that it does not hold the gun in place particularly well when you are in compressed and entangled spaces. That is why I have strong doubts the person the OP was talking about has done any legit FoF work with truly resisting opponents with focused oppositional will, malevolent intent, and freedom to act as a bad guy really would act. 7 out of 10 times in any kind of entanglement - standing or on the ground - the gun will absolutely not be where you think it is, not will it be in a position that you can easily access and deploy it. I have worked extensively with a clipdraw because years ago I thought it may be a good solution. I can back up what I just wrote with years of testing and a metric ton of evolution repetitions with many people. When the guy spouting off he is good with it in a grappling situation, until he posts multiple video, I won't believe him.