Or you have never been shown by someone who could actually do it in a decent way?
For the record: I haven't seen/felt much myself with regards to fajin, but I'm curious what makes you so sure it's impossible to pull off a fajin with the dantien to mingmen against even a decent high school wrestler. If you'd say that it would just take to much effort to get a decent fajin with the dantien to mingmen to be worthit, that would be something else, btw.
I find that the extreme backbow training is useful for more than just power-- also to gain awareness/conditioning of the use of the backside to off balance someone. One doesn't have to make some giant backbow movement to get this feeling, once you have trained it for a while.
It's one thing to have shenfa (body skill) ,but fighting in a modern striking environment means dealing with boxers who train their accuracy and target recognition on focus mits. Someone like that can be very dangerous, in my experience. Shenfa or no shenfa.
The real question, as I think you alluded to, is , what are a person's goals? There's only so much training time.