You've made some great points in this thread; your knowledge of the ins and outs of this game is vast and I'm not going to question any of the recent points you've made.
With respect to this daytrading vs. training in lower divisions, I don't think you're looking at the entire picture:
1. Daytrading is too time-intensive for the average user. Also, with the new transfer rules and lack of funds available to new teams, this option isn't all that realistic.
2. At the D4 and D5 levels, it's hard to screw up training: avoid JS, focus on OD, and sprinkle in a little PA and 1v1.
3. Training your own players accomplishes two things:
a. You can use all of your profits to build your arena and increase income.
b. Your roster is more valuable than the weekly salary paid.
4. A team's value isn't solely determined by TPEs of it's players. Arena size plays a part as well.
Hrudey's team
(30851) is a perfect example of what 2,3, and 4 can do in a short amount of time.
Strictly focusing on training has allowed him to put 1.5 million dollars into expanding his arena. This is only in 2 full seasons, mind you. Pretty impressive. It's not like he's been one position training, either.
His low team salary, which his team vastly outperforms, allows him to pull 110k in weekly profits as he earlier reported. He's going to have a serious nest egg when he promotes to D.3.
Contrasting this with you're friend
(30254) shows how advantageous training can be, even if we take into account his recent inactivity.
Even for a more average user like me, training has been profitable. The painstakingly anal process you went through of ripping apart my transfers ignored the fact that non-NT caliber players still have value. Each of the players I sold were more than capable of capping, which is why they sold for the prices they did.