the Jester
Legend
The argument always was that it was ninth level because of the speed rather than the power.
Wait, when was this? Can you cite something to demonstrate this? Because I never thought that was the case. Power words are high-level spells because they are no-save devastating effects.
Also, casting a power word has always taken the spellcaster's action throughout D&D history. I don't know if they exist in 4e- I can't recall seeing them- but if they do and only take a minor action to cast, you might have a case.
But personally, I think the power words are plenty strong without becoming bonus actions. Lower-powered versions, maybe.