Don't get me wrong. I feel sorry for you even though I think you are largely responsible for your misfortune. Nobody would like to be in your position and all of us have been through (and are still going through) the struggles of trying to make a success of this industry.
I am surprised, to put it politely, that after completing ATPL theory, CPL/ME/IR training, MCC, maybe JOC, and 500 hours of professional type flying, you cannot calculate pressure altitude. I think you're right that there are gaps in your knowledge. Perhaps the reason this surprises me is that my, and some of the other posters, training backgrounds were of a higher quality than yours. This completes the circle that others have mentioned of airlines wanting to recruit products of known quality training, and that by taking the shortcut of P2F you may have 500 hours but not quality training or experience. You can buy hours, but you probably can't buy a job.
Additionally the magic 500 hours on type is normally a filter to thin out the tsunami of applications that any job ad normally receives. If everybody buys 500 hrs then the filter will be set at 1000 hrs, then 1500 then 2000 - you get the picture. At that rate you could hit mandatory retirement before you ever turned a profit in this industry. 500 on type may be a common filter in the job ads but with less than 2.5K to 3k you'd be struggling to find work. Would anyone really pay for that much P2F? Where does it end?