I learned to fly in the mid-90's. I went to a 4 year college and then instructed afterward. It took me a year of instructing to get the 1100 hours that regionals were requiring at the time. Yes, the hiring minimums were 1100tt/100me for most all of the regionals in the late 90's. And it only took me a year of instructing to build that amount of time. So you saying that it takes 3 or 4 years of instructing is just not true.
The real reason pilot starts are down was touched on just a few posts ago. It is the extremely high cost of training. I believe it was shortly after 9/11 happened that training costs skyrocketed. I don't know if it was due to insurance requirements or just greedy flight schools. I think a little of both. But it has nothing at all to do with the ATP requirement at 121 carriers. People just can't afford to drop the kind of money that it takes to get your CFI's with the end result being a job that doesn't pay enough to pay back those student loans.
This is the power of the internet at work. People are just more informed today than they were back in the 80's and 90's.
I just reread your original post and came across this, Getting 1500 hours in order to be allowed to knock on a door for a SIC job would take 8 to 12 years, . Why would it take 8-12 years? That is only flying 125-187 hours per year. Who does that that is trying to get to an airline? NO ONE!!!