Yeah, I have both platies and mollies and mollies do get bigger, and they are more active and "busy" where platies tend to stake out a certain area, and just do their thing there. I personally would not put anything else in it.
ETA- Plus, if there is any female there, they will most likely at least have a few batches of fry, which will add even more to the mix.
My bettas: D'Argo + the girls Jullanar, Lalla, Razz, Rayleigh, Aviendha, Arya, & Lovelylocks
plus the other guys Toni, Eli, and Clinton (platy, guppy, and molly) a kuhli- Burt, 2 yoyos- Duncan and Ma, and otos, Laurel, Hardy, Larry, Curly, and Moe, plus the kitty, Clara the Impossible Girl.
SIP: Turk (teal VT), Azul (royal blue VT), Jerrica Benton (pink cambo CT), Lady Amalthea (blue cambo CT), and Jadzia Dax (blue VT)