Subfloor question

I am currently renovating the upstairs of my house. I originally had carpet throughout the upstairs and I will be converting to hardwood. After tearing up the carpet, the subfloor is MDF so I purchased 3/4 plywood to lay on top but have yet to install it.

I just noticed afternoon doing some random work upstairs that the mdf looks to be 1/4” mdf and there is actually a layer of 3/4” plywood underneath.

Is it ok to install red oak hardwood flooring directly on top of the existing MDF / 3/4 plywood? Or should I put down the plywood I already purchased? I’m just afraid the joists won’t be able to hold all that weight now. I have 2x8 joists...