To be really bold, I will say to anyone, without ever having touched them "If you train in 4 or 5 arts at the same time....You suck!"
And I have never been proven wrong.
you meant all these grand masters who are masters of dozen different arts are kinda sucked? come on now! don't you think that underwater-basket-weaving would go well with aikido? what about okido or deja-fu or mamboryu? surely they would go well with aikido.