Well let's discuss this then.
Which classes/specs were not viable for raiding for Hybrids, what patch cycle/raid was affected, and what is the expectation (your opinion) of what Hybrid Tax should be in terms of viability.
The thing about Hybrid Tax is that it's basically on anyone that has a heal spell. As some have mentioned, even Warriors are hybrids considering they can Tank and DPS in the same way that a Hybrid would be able to Tank and DPS. The difference is the tax is on those who have heals, considering a Warrior DPS is not being taxed (heavily) just because they can put on a shield and off-tank when the situation calls for it. For Hybrid DPS/Tank, the gameplay doesn't support them healing while performing a DPS/Tank role. Shapeshifting alone takes up 30% of our mana! Heals take up too much mana or are infrequent enough that they aren't sustainable when you need heals.
To be clear, I'm not saying Hybrids should deal equal DPS to a Warrior or Pures because 'they can't heal in their DPS specs'. I'm pointing out that 'flexibility' doesn't exist when a Hybrid DPS/Tank can't heal effectively (or at all). The stats simply don't support flexible healing gameplay. If it did, then we can talk, but until my Feral Druid can cast his free-heal procs in Cat Form or shapeshift doesn't take mana, then there's no reason to have heavy Hybrid Tax as it existed pre-1.12. The Int and Spirit on Pally/Druid gear doesn't make off-healing viable, and the Str/Dex doesn't help healing at all. It's a 2-way tax for a gameplay style that simply doesn't exist.
https://www.mmo-champion.com/threads...1#post48668908
This post outlines the problem clearly. We are being taxed for something we can't even do but everyone thinks that we can.
The direction in TBC happened to be 'Hybrid DPS can't effectively heal, therefore we won't tax their gear with Int/Spirit and give them stats they can use'. This included making each point of Str and Agi give 2 pts of damage (like pures) rather than the hybrid tax of 1. If 'Hybrid DPS should only be flexible Support because they have heals' is the core design we want to keep, then I think Hybrid DPS should be redesigned to effectively perform heals while DPSing. Right now in Vanilla, neither of that exists, and the design doesn't support any Hybrid gameplay other than pure Healer (pre 1.12). The tax needs to be addressed, that's the point because the design doesn't support it.
The tax was not only on Tank/DPS but also on Healers (Str/Dex wasted on gear, lack of +heal plate/leather early on), which made our core support abilities the only reason to be brought since we were so inefficient at everything else we did. That would be like putting a tax on Mages for having Polymorph CC, then bringing them to raids only because they offered that unique CC. It's not a case of 'well everyone is not viable' or 'not everything is equal and fair'; rather it's an arbitrary design tax where it doesn't exist elsewhere. Mages can't heal, true. But neither could Hybrid DPS.