You are most completely right, sir, i want those specific Powers because of the Action Economy. The problem being, when i'm raging and on Melee, if i use Schism, then i can still use standard action powers in order to control the battlefield around me, including using powes in enemies that i'm currently in a grapple with. Hustle with Schism allows me to initiate a grapple with a Full Attack + Pounce, and still retain my move to break the grapple and reposition myself, or, it allows for charges to be made outside of a straight line, by repositioning with Hustle+Schism and then charging as a Full Round Action. Synchronicity with Linked Power is where the abuse lies, but i'm not taking Linked Power. Also, many of these tricks will not be available for me early on because of my reduced ML. Temporal Acceleration won't come into play much later, but when i do get it, it's for the same reasons as any Wizard wants Time Stop... It's just silly good.
For a grappler, i could, of course, have gone with straight druid or a wizard grapplemancer, but i've been meaning to try out psionic, and the thought of an Octopus psionic grappler that ISN'T an Illithid is very appealing. There's of course, the VERY useful fact that Psionics give me access to EXPANSION, which i can use to grow two size categories instead of one, and the fact that it doesn't use somatic components, so i retain full use of my powers even if i'm currently in a grapple.
The Substitute Powers ACF is of course better than the Expanded Knowledge feat, but you already knew that
. The thing is that the Time Mantle has 7 powers and the Mental Power Mantle has 8 powers, instead of the 10 powers some of the other Mantles add, but allowing it or not is up to you. Next mantle i'd take would probably be Natural World in order to access Metamorphosis, and i'd probably ask you to allow Greater Metamorphosis to be added into the Mantle with Substitute Powers, since it does add Metamorphosis and it only has 9 powers in it. Or the Freedom Mantle for more battlefield repositioning shenanigans... It all depends on how you want to go with the Substitute Powers ACF!
As advancement, i'd probably stick to Ardent until i could qualify for either Sanctified Mind or Slayer PRC, which grants Full BAB, and then stick with those until the end.