Quite simply, anyone who is spending their time in such shenanigans trying to cause their character to become ridiculously OP will quickly find themselves having a visit from one of the characters left in the universe strong enough to eradicate them with ease, like say Demon King Piccolo. Also, while Zenkai will provide a decent boost it will not be huge, I am thinking more like five to ten percent of the current PL, rather than thirty percent.