Tbh I don't see a problem with having tripple spec if there were boundaries to it -
The 1st boundary would be whether the spec is fo PVP or PVE purposes.
If you choose it to be your PVP spec, you will not be able to activate it during a 5 man dungeon or a raid instance.
If you choose it to be your PVE spec, you will not be able to activate it during Battlegrounds, Arenas, or World PVP zones (TB and WG) - PVP Servers will act the same (No boundary for 'normal' world PVP)
The 2nd boundary would be that you can not have multiple specs of the same specialization per play type, example:
A warlock with 3 PVE specs would need to be Affliction, Demonology and Destruction.
A warlock with 2 PVE specs and 1 PVP spec could have Affliction, Destruction (PVE) and Destruction (PVP)
As for how Blizzard stated that people would use this system to create perfect builds for each fight, then yes I guess it would - but why should that matter? For hardcore guilds the best option is to optimize every player to perform at their highest abilities in each fight, some will probably go back to their trainer and respec simply to do that anyway. Having this tripple spec design just makes it more convenient and means less time waiting.
Raids that are not as focused on progression and simply want to have fun are not obliged to respec to a more viable build for specific fights simply because its better for that fight, but they have the option to if they enjoy all 3 specs.
anyway... just my opinion