But he's opining on how Comps are the best way with no direct experience, and by having actively chosen to have his own children avoid them.
How has he actively chosen to avoid them? If he is in a grammar area, then presumably, there are no fully comprehensive schools that he could have chosen in any case.
Personally, I find it quite convincing when someone who is in a position to benefit most from an unfair system argues against that unfairness.
You can disagree with the existing system while still wanting the best f for your children within that imperfect system.