Even assuming that 100% of the return air came from the basement, the coefficient of performance for cooling purposes would be abyssmal. You're essentially using the uninsulated basement slab & foundation walls as a not very efficient or effective heat-exchanger to the not-super-cool sub soil, while burning 600-1200 watts (fully inside the house, no less) to move that air around. The net effect is to even up the basement temps with other rooms, but adding 2000-4000BTU/hour to the house in the process.
And if you're not drawing 100% of the return air from the basement, you're using yet another ineffective inefficient heat exchanger to the mix- the (best case sealed but un-insulated) basement ductwork, which has even less surface area than the basement floors & walls.
And if the ducts aren't perfectly sealed & balanced, and you house isn't the tigthest house in the state, you'll be driving infiltration of (potentially hotter, more humid) outdoor air into the house at some unquantified rate.
While moving all that air may even up room to room temps it does next to no cooling, but the moving air may add to occupant comfort by wind-chill on skin. The same effect can be had with much lower power with fans in occupied rooms only.
Alternatively, expending 600-1200 watts on a room sized air conditioner (or better yet, a mini-split) in the hottest rooms of the house would actually remove heat & humidity from the house rather than adding it.