All you can do is show them daily that your lockdown is a more effective form of half guard. If your getting sweeps, they can only talk shit for so long.
Trust me I wanted to say that, but fuck it man... I'm not going to say shit just go with the flow
I just know he's been doing bjj for a long time now, if I remember correctly he is a brown belt, however he's not the gi instructor just runs the no gi class.
Maybe you should just pick his brain about why he dislikes the technique then? It would be unfortunate if your relationship just consisted of his ridiculing your techniques while you contemptuously lose faith in his opinions.