There would be so much more possibilities in this combat system if maneuvers weren't part of the PVP deck. You're forced to have moves to generate IP, attack, and defend which doesn't leave much room for maneuvers. Being able to switch between maneuvers would make it so a lot of other skills can be used in decks and would allow for a lot of counterplay in certain situations.
For example, lets say I'm getting chased 1v2 and it's a fight I'd like to take, however, they're currently behind me hitting me. I have no way to stack IP on them while this is happening so I'm basically forced to just get dunked or try to clip them on some object so I can take aim spam. If I could instead just switch to Death or Glory during this time I would be able to build IP and then switch to combat med or bloodlust or something else and fight back after. It's pretty much impossible to build enough IP in such circumstances as the take aim CD is way longer after each use and with people hitting you if you can't use a defense for 20 years you're going to get dunked.
There isn't really any negative side from having the maneuvers separate. It'll just make the PVP system way cooler and more advanced instead of people following a certain meta. It also wont take 30 years to get IP because think could be a useful skill again too, it's currently impossible to fit it onto decks with all the other shit at the moment. Quick barrage would continue to be useful too as usually you're forced to swap it out with other moves.
It'd also be cooler if the take aim/think CD on higher IP was reduced significantly. It is WAY too long.