The Espada wouldn't be able to do well at all unless there was someone with Urahara's expertise to use their Hollow essence to poison the Quincies in some way. Szayel is not on that level and Aizen hasn't shown any tech-prep skills and he already has admitted inferiority in intellect before Urahara. Both of them need knowledge of that hidden Quincy weakness anyway.
Anyway, the Espada wouldn't do well because there are already a few people among the non-Elites who can solo the Espada, like a full-power Mask, Gremmy, and Royd Llyod. Throw in people like As Nodt, Bambietta, Robert, Bazz-B, and Pepe and the whole Arrancar army will be crushed very quickly. Gin isn't above top Espada level, and the only thing deadly about him is his Bankai, and several Sternritters could probably react to its normal extension speed or handle it in some other way. Same goes for Tousen.
Aizen is strong, but he hasn't put any of the Sternritters except for possibly Yhwach (and even then this is disputable) under Kyoka Suigetsu. In his base form, there are several Sternritters who can take him out like Gremmy, Royd, and the four Elites. Aizen isn't beating Yhwach, and he won't be able to force him to use his Almighty Eyes (though if he does, then Yhwach can casually solo all in Heuco Mundo). Yhwach is also a superior war strategist, so if he's the attacking side in the invasion, then Aizen's forces will be effectively crushed. Yhwach probably won't even get to sleep before everyone dies.
