1/ Matrix cubes suck compared to PvE & PvP endgame relics, any clever person wouldn't be stacking a mainstat in any of their relics.
2/ You should never take into account the person is fully buffed and stimmed before asking for a inv. I usually pop my stim and buff in the instance to make sure they aren't wasted.
3/ 6-9% skill tree buff is not available for all classes.
4/ You still fail to forget people who stack secondary stats rather than main, my sent who's 2/5 dread guard rest campaign sits at around 1900 strength and around 1000 power, it I removed the 12 might augments and replaced them with power I'd only have 1700 strength but 1200 power. By your main stat rule that would be too weak despite my character being far over-geared for a story mode.
I am accounting for augments and earpiece, my dreadguard/campaign sent is only over your 1800 rule because I stack strength augments so I don't have to stack extra crit in my gear where power could go. Most my gear is optimized for power rather than mainstat.
Because you're not taking account on secondary stat optimizations, plus you're adding a stim on top before you enter the op, without a stim your sorc would only be touching 1800 in rakata which most rakata have the main stat heavy 25a mods in. If you're asking people through chat unless they just come from an op and still have a stim running then they are not going to pop one just to check their main stat.
TFB is balanced for players in columi 136 rated gear, by requesting people have at least 1800 main stat all you are doing is bringing overgeared players for an easy ride.
Also just FYI, here's a quick columi build I made on ask mr robot, I even included a stim yet it sit's below 1700 despite being in full columi and ready for the content, full columi without the stim is around 1500 strength not the 1800 you picked out of your head.