In all honesty though, the only people who would have a problem with that solution are the people who arbitrarily claim you shouldn't ban an ability on one mon. I'm making a somewhat big assumption in saying everyone would be okay with a non protean greninja. If protean greninja has to go, ok. If a better solution was banning protean on only greninja so it could be used,
I would say you can go pound salt for not wanting to do that.
That is like having a problem where you constantly smash your fingers whenever you open a door and close it. Your options are to either exist smashing your fingers, or removing all the doors in your home so you can't. But you will be very cold during the winters among other problems I'm sure we can imagine. However, there is another,
crazy option, in which we simply wear gloves that can stop the damage to our fingers. ArVaDa-, that is convoluted, who in the right mind would want to make gloves like that!? Someone who is tired of bloody fingers, or poor living conditions, I would think.
I'm not trying to be silly here, I'm serious. We are preventing a mon from being used because we can't do a ban
that complex. What the heck is up with that? I remember drizzle + swift swim being banned somewhere. And I remember some tiers just not allowing weather at all leaving you with a water absorb politoad or flash fire ninetails versus banning them into the upper tiers. You're telling me something as significant as greninja, something that is so annoyingly good we even went and banned it to save our metagame from being "crippled", that it is somehow not completely like a weather ban? I am utterly dumbfounded.
Now this is pokemon, I really don't care that much about our froggy friend, but I care enough about this ban system that I am willing to write a paragraph or so about how silly it is. I know there are plenty of people who would like to try to use a non protean greninja because of its speed and can't because it was "burdened" with having protean. It honestly is kinda like serperior without contrary, yeah who cares it isn't all that great. However, there are people who would like to have this frog as a pet to use in combat, and by golly not letting them have a cheap knock off of it is just evil. Same with blaziken and talonflame, yeah, so what if they're outclassed if they don't have a sweet ability, you should still be allowed to use them to embarrass your friends. I can use arbok on poison if I want to, and I can think of a myriad of things that outclass it too.
tl;dr Something is wrong with you guys arbitrarily saying we can't do one thing or another. I would imagine the only response to this is that this is such an insignificant complex ban there is more work than use in changing the way things are. I would be damned if someone tried to tell me a non protean greninja couldn't do something, outclassed or not. I think
EmilyBay had the right idea from the very beginning.
Note: Potentially this system isn't entirely silly. I could imagine a problem occurring where if the pokemon are tiered, like Ubers to PU, that abilities could become very complex in tiering. Yeah protean greninja is uber, but maybe non protean is UU, so can we have greninja in our UU tier and above if we limit the ability? That
could be done, but it would be a rats nest. We have one tier, monotype. Something is banned or it isn't, a complex ban here is not nearly as ridiculous as it could be elsewhere (however they have made exceptions with pokemon such as politoad in the lower tiers, so I would say even then this banning system is still not very true to itself).