Technically DSC is a lossy form of compression. VESA claims it is "visually lossless". I certainly can't really notice any compression artifacts. During static images and probably low framerate content, there should be no compression artifacts. In high framerate content where frame to frame changes are significant, there is potential for compression artifacts. But it's going to be hard to notice. Especially on LCD displays where response times are slow enough to hide some of the frame to frame variation. Even on unnamed faster displays, it's probably going to be hard to notice without BFI. Even with BFI, it'll take a keener eye than most of us have.I don't believe the display port 1.4 connection has any perceivable loss or lossy compression. At least not to my eyes. I would just go displayport 1.4 with dsc @ 144hz and not worry about a thing, which is what I did.
This explains a good bit about how it works: https://www.quantumdata.com/assets/displayport_dsc_protocols_webinar.pdf
Now in the case of the Gigabyte / Aorus monitors, the HDMI port is limited to 24gbps, so no matter what input you're using, you need DSC to get the high frame rates and bit depth. A full bandwidth HDMI2.1 port can transmit an uncompressed 4k120 signal at 12-bit (but not 4k144). And DisplayPort 2.0 should be capable of the same. But there's going to be continued demand for higher resolutions and refresh rates. The bandwidth required for uncompressed signals is pushing the limits of what we can do with copper, so DSC type technologies are here to stay.