Do people not go Te/Fi? I don't either, but it should be a more general aoe combination that is still even close to Te/Su single target. Only problem being that it ends up getting replaced by Techer/Phantom.
Regardless, TEC is a great stat to go for on anything but Te/Hu and Te/Ra. DEX is acceptable for subclasses that have the appropriate mag skill.
Fo/Te is a much better tech casting class than Techer, and Te/Fo is not at all redeemable. But if you want to have high TEC for both melee and techs, then go Te/Fi or Te/Su.
Summoner sub is extra useful in the early game due to stat increase skills you end up taking that you wouldn't generally be taking on other subclasses, which will help you equip better gear earlier than you normally would.
While I'm probably in agreement with Lapinoire about Te/Hu being generally not as powerful or useful as other combinations, I don't really like the idea of calling it a crutch, but it definitely is true that the main reason to take it would be Iron Will as well as Hunter Physique. Te/Fi and Te/Su (with Summoner's Mark) should definitely be dealing more damage, and Techer Deband actually acts very well on its own as a way to increase survivability.
As far as I'm aware, Techer's Photon Fury explosions actually do get amplified by Hunter's skills. Te/Hu is superior to Te/Su when it comes to damage without the use of techs or Summoner's Mark. Te/Su's high base stats help alleviate the difference in terms of multipliers, as it counts towards your Shifta increase, but it doesn't count enough to even out the difference.