She's weakened, or more accurately holding back her strength intentionally because she doesn't want to break an expensive national treasure again (there's a flashback of her chibi form breaking the same spear). Makes sense to me even though the phrasing could be better.
Thats because she's the one who's around most since shes our MCs trainer and very horny lover. I am sure the other mama's will shine once we have more time with them.
HAHAHAHAHAHA! Oh god! I love how the artist made Maniannas daughter look on page 10! Its hilarious! I hope once our MC finishes his harem of mamas she'll along with the other children accept him. Though they probably won't care considering how this world treats moms as if they are expendable furniture.