So basicali squad lvl scales ALL your mantics and waifus up so they are ready for combat (their stats grow with squad lvl) .

Individual waifu levels DONT give them stats.

HOWEVER the squad level is determined by the HIGHEST lvl waifu . So if you want to power level your team focus on leveling 1 waifu first .

If the leveling is really slow then you schould move to the next area that has scaled up rewards or just use your other low level waifus because at that point the high level waifu wont get much lvl progress anyway so go nuts and have fun with the rest of them : )