Generally, as a personal rule, I don't LH tech stop. The yields are far less. As most of my tech stops are losing money. (Mostly from SXM base)
This is also quite evident in my DoTM airline where my tech stops routes are killing my airline every day.
Back to JA. LH is very different from SH. Once you go beyond 4000nm, LH changes from flying 1 daily to less and less rotations. At that point, C/F class become extremely important and the ability to take as many pax as far as possible becomes paramount.
I am not sure what the answer is for the tech stop troubles your having. Indeed tech stops should be more expensive then there non-stop counterparts (fuel wise), however there's probably a bug somewhere in pax calculation that prevents tech stops from achieving max LF% using typical strategies.
Perhaps you should kick a bug report to Sami and get him to weight in on it?
Btw, my dash 61s make north of 350k a week. Even those ZOMG fuel hugging Il-18 props still turn 2-5x there breakeven profit. I bet the biggest losers are the Comet and SE-210 fliers. Probably 701, DC81s and DC82s are not far behind.