They don't need a shit load of time to utilize it when they have gotten a hang of their power like Devana or current Deryl who could pull out his mech in an instance.
MC hit her because she thought Shen had had him and had lowered her guard. Also remember that while she was tag-teaming MC she was also not taking the fight seriously and was only using a fraction of her power, as stated by Syla. Also that's not how split traits work.
What she lacks isn't power but battle experience and a proper battle mindset, considering she had only been an SH for a month, but that could be easily fixed after the time skip.
Deryl has his stone and his stone allows him to create all the things he can create near instantly. He and her would still get pwned by 9 of the 12 trait members. Time would stalemate. Only Body, and Memory would have difficulty against him or her.
Syla said that is how Split Traits work in one of Dream World's first scenes. Something like, "You've been spending too much time training your Daddy side. Now you need to train your Mommy side." She straight up says that MC cannot maximize his potential unless he masters both sides of his power, which he didn't before that fight.
I agree she doesn't lack power. She lacks battle exp and a proper mindset but I disagree on that being easily remedied, She lives in a dimension full of monsters and still decides to half ass train. Her almost dying to MC who's double teamed and getting head fuck sniped by a level four while a twin boosted greater spawn who she's match-up predisposed to beat is a terrible performance. Fucking around or not, back then, 1v1, he would've mirked her. You don't fuck around this deep into the game. She's literally one decent hit, one kill. She has no survivability whatsoever. She coasts off her circumstances while training like JV athlete when this is the Big Leagues!
She will be substantially stronger when they return to Earth.