Any time you can do a GCD on a target and not use form shift you're gonna do more dps. Period. It's also not a viable way to conserve tp. And considering you can generate an extra 700 tp every two minutes you should have almost no problems sustaining tp if you manage your chakra stacks and use purification and invigorate appropriately while knowing when you can or can't spam out rockbreaker or arm of the destroyer.

tl;dr don't use form shift if you can actually use that gcd to do damage; use meditate to build up stacks for purify instead of using form shift to conserve tp.