This is true, I was actually thinking that a refinement to the proc'ing system would be in order. As it is right now, you're correct. None of the systems in place are perfect.
This may be a bit scatterbrained, but this is something I was thinking about in terms of improving the proc system as a whole.
Since SE is going to be revamping Nyzul Isle in the near future, I'd imagine Mythic WS's are once again going to be pretty commonplace (not that they were rare to begin with.)
They could make a sort of hybrid system between the Blue proc'ing in abyssea and VW's system.
General Rundown:
You have 2 different ways to proc with weapons, NQ weakness and HQ weakness. The NQ weakness would be a generic WS that most jobs have access too. HQ weakness would be Mythic WS's. Every job has one.
The difference between an NQ and HQ trigger would be the increase in drop rate on desirable loot. This loot still has a reasonable shot of dropping with just TH (which makes the entire system somewhat optional, but still gives incentives for trying to incorporate it into your playstyle/alliance make-up.) But the NQ trigger would increase drop rate significantly, and the HQ trigger would make it near guarenteed.
Keep the whole "time aspect" of blue procing from abyssea intact.
Weapon types that have no Mythic WS at all would be removed from the list entirely.
Example: Let's say... you have Polearm. NQ weakness would be something like Raiden thrust: DRG, SAM, PLD, WAR, etc. have access to. But to trigger the HQ weakness, you have to use the Mythic WS for that weapon type: Drakesbane, a DRG exclusive. This way, even if a DRG is not dealing as much damage as a SAM or WAR (purely hypothetical here...), he compensates by giving out better loot during Piercing time.
Other example: A weapon like Sword, which PLD/BLU/RDM have Mythic WS's for. All 3 would be able to proc HQ weakness. Guarenteed. This way, during Slashing time, if it happens to be sword, the RDM/PLD/BLU have it covered, all the while covering NQ weaknesses for other damage types when it's not Sword or Slashing time.
The way I see it, it means that every job during their specific time has a reason for being present at an event, but if people choose to just bring <insert top DD here> to their runs, those players aren't completely screwed. They can still do NQ procs with other weapon types during times where their HQ proc isn't a possible option.
It's entirely possible that I may be overlooking something that makes this entire idea stupid, this was more of a "top of my head" thing. Just a thought. Either way, it's late. And I'm gettin some sleep.