I have said the same thing about ex-Adventists; how that they are not really “experts” on Adventists either.
After being on this forum for close to two years; I do have some reliable knowledge of Catholics; however, as I am constantly told here;I “do not correctly understand.”
I don’t look at myself as an expert; however, I can say what I do know.

I find it hard to believe that all who leave the Catholic Church do not understand it well. I would say that your statement in the OP is just an anecdotal assertion. Maybe some who leave your Church do understand, and just maybe thats why they left. I believe that this is so for some who leave my Church, and there is no credible reason to see it differently with your Church. Very often, people do not even leave a church because of doctrinal disagreements.