The ACA is grounded in a lot of political policy going back to the Nixon era, and draws from quite a bit of conservative ideas. The individual mandate itself, for example, was a Heritage Foundation proposal from the late 80s, and was ironically one of the main targets of Republican objection during and after the implementation of the ACA.

If you review Nixon's CHIP proposal (https://www.nixonfoundation.org/2015/11/the-nixon-comprehens...), you'll find a proposal that maps pretty closely onto the ACA marketplace that we now have available.

"Mostly shaped by Democrats with major proposals cribbed from Republicans" would be a more accurate assessment.