Popa: Not really. The Gemara and Rishonim already say that Geirim have a high rate of leaving. That’s not a failure of just Z’man Hazeh.
I’m not sure what the rate was back then, and how it compares to what it is now.
But it seems too bizarre that a rav would continue using the same parameters to measure something after seeing a hundred times that it doesn’t work.
We aren’t doing anyone any favors by making them jewish and then ??????. If we really care about them, we should stop doing that.