So I guess the RS is just a temporary PU? Sanji's true PU is his exoskeleton and possibly Lunarian DNA awakening? He's already very powerful with his modified powers since this exoskeleton doesn't only boost his durability but also his physical power as Reiju was already able to dent steel when she was a kid.
It was clearly shown by Oda that Vinsmokes are at their fighting "peak" with Raid Suits on.
Exoskeleton just unlocks Sanji's gimmick which is probably going to have something to do with durability/defense so he doesn't break his bones while kicking Veterans anymore.