You have a 45k salary level 5 trainer that you paid 80k for.
I have a 10k salary level 4 trainer that I paid 30k for.
Lets assume that a level 5 trainer gets 3 weeks extra training per season than a level 4 trainer.
Lets say the season is around 12 weeks long. (Not sure exactly how long it is, I think it is 11 weeks + playoffs).
Straight up you have paid 50k more than I have.
Then each week you are paying 35k extra than me.
35k per week x 12 weeks in a season = 420k.
I'm not sure how the salary increases, I'm assuming that are salaries increase at the same rate for simplicity, but chances are your salary will increase by a larger amount each week than mine. So when mine is at 20k yours is at 60k or something like that.
If you take in to account the salary increases, you are probably spending 550k to 600k in the first season more than me.
Lets take your assumption that you are training 2 positions. So you can train 6 players at 48+ minutes potentially (although its quite likely that there will be weeks where only 5 players get trained).
It is highly unlikely that you will get 2 pops per player in those extra 3 weeks training time (and also it might not even be an extra 3 weeks training time, it might be less). But let's be generous, and say you get 9 pops between 6 players (realistically you probably only get 7 or so depending on what you are training).
Lets average out the pops over the 6 players. So basically for 550k extra you get 1.5 pops per player per season.
1.5 pops per player is not likely to increase the price of each player enough to cover the 550k that it cost to get those pops.
Also, I will have 550k, on top of any other money I might have earnt, and I could buy a million dollar player with great stats.
So end result: You end up with 1.5 pops per player per season that might but might not cover your costs of the trainer, or you end up with well trained players that have 1.5 pops less than they could have had, but an extra 550k that could easily be used to buy a great player that will help your team a lot more than those 1.5 pops per player.