If someone could show that paying a fair wage to workers would still leave solar compellingly cheap then it might incentivise some parts of the supply chain to clean up their act. That's "if" of course.
You can be certain that forced labor would be considered a "subsidy", although I don't recall ever having seen it mentioned in these filings, so my inference is that it's not a significant factor.
The last one I examined in any detail was https://www.federalregister.gov/documents/2023/07/11/2023-14..., which imposed a 10.33% countervailing duty on Jinko panels, a 14.27% countervailing duty on Risen panels, and a 12.61% countervailing duty on all other PRC panels. This was enough to ensure that under 1% of panels sold in the US were Chinese solar panels.
But we're talking about competitiveness with fossil fuels here, which are about 200% more expensive than solar power, not 14.27%.