You seem rather alarmist. Not every class benefits from their mastery 100% of the time, not by a long shot. Blood DKs only benefit when they death strike, and can't maintain it 100%. Frost DKs only benefit on their mastery on HB/frost strike and not Obliterate, which really sucks for 2H frost. Boomkins only get benefit from their mastery when they're in eclipse. Only bleeds benefit from ferals mastery. Rdruids literally have a buff to maintain just like us to benefit at all from their mastery. Guess what they need to do to maintain it? Stand still and cast a direct heal. Even if you want to exclude the "partial masteries" which only benefit certain abilities of a spec (IE SV *and* BM's masteries), you have masteries like: Fury warriors only benefit from their mastery when Enraged. Rshamans and arcane mages have their masteries fluctuate based on percent health of the target/percent mana respectively. Maybe Arcane mages should argue they should have full benefit even when they're going OOM. Hell, have you seen a MW's mastery? It summons spheres which other players HAVE TO WALK THROUGH. Talk about being useless. Sub rogues mastery only benefits their finishers, assassination rogues only benefit their poison attacks, elemental shamans mastery is literally a %chance to summon a duplicate spell, so they only get 100% benefit from their mastery when they stack mastery to 100%.
Yet you insist we need to have a mastery which, and I quote, "benefits from 100% of their mastery 100% of the time..." So I ask...why? Our other two specs don't even benefit from 100% of their mastery 100% of the time.