I agree and have also been a victim of the so called "con artist" coaches. However, I think most of them are conning themselves as well. I would give them the benefit of the doubt that they are actually trying to help, and genuinely believe that they know how to teach golf even if they can't play that well themselves.
You should find better instructors. Ones who actually play to a decently high level. Not all good golfers can teach, but there are certainly enough good golfers that some of them (like the ones on this site) can teach well.
In regard to your 125 yard +/-10 foot statement:
If you hit your gap (50 degree) wedge within +/-10 feet 125 yards away, then you should be able to make any standard par 4 (375 yards) within 3 strokes. This would leave you 2 putts for bogey. Most of the time 10 feet would give you a little less than a 25% chance of getting par. So, on a typical course with 14 par 4 should give you on the order of 12 strokes. Par 3 and 5 similar thing. So, you should be able to make on the order of 14 to 16 over par which is something like a 12 to 14 handicap with just a wedge and putter.
Erik brought up that this figure is about 2/3 closer than the best PGA pro in this distance range.
There is also an implication that being able to hit your gap wedge 125 yards generally means that you can hit your driver on the order of 250 yards. The same swing with a properly fitted driver should give you 250 yards with a commensurate accuracy with the driver or about +/-7 yards. The usual rule of thumb is that a person who can hit a PW (47 degree) hit 120 yards (carry) can generally hit a driver 240 (carry).
Edit: agree with @mvmac.
I hate to get into these types of discussions about what a person can and can't do over and over but I will just say this. I am seeing a LOT of guys that post their shots that are immediately "debunked" by posters on this board. Let me say two things regarding your statement.
1. If I'm at the driving range and have hit a bunch of balls and get dialed in on a couple of clubs it is not only NOT hard but it is sometimes even pretty easy to hit the same shot over and over. Same club, same swing, same tempo and pretty close to the same result. 10 feet front, back, left or right is really not that hard to do if you are repeating the same swing. As I said before the reason those statistics don't really apply when talking about the pros is that they are going from Driver to maybe mid to short iron or wedges on approach shots. That is not the same as making the same swing 30 times in a row. I think that most all pros could make shots closer than 10 feet if they have hit 30 balls or more using the same club on a practice range.
2. As far as that formula measuring approximate club distances for all other clubs in my bag using the 125 yd gap wedge, if I swung every club exactly the same then yes you might be close. However, that swing that day was a well rehearsed, relaxed swing that I had been working on. I can honestly hit a gap wedge further than that if I wanted to. When I'm on the range I can get my tempo pretty dialed in because I am hitting a million balls but when I'm on a course not so much. My tempo can be faster to too fast causing mishits or even slower than what I used on the range.This is why I don't hit hardly any GIR when I'm playing.
So basically don't use that particular shot to approximate my distances because it would not be accurate. My distances are not consistent in any way at this point.