>as it will allow drives to run in MLC or SLC mode instead of their native QLC

That depends on the SSD controller implementation, specifically whether it proactively moves stuff from the SLC cache to the TLC/QLC area. I expect most controllers to do this, given that if they don't, the drive will quickly lose performance as it fills up. There's basically no reason not proactively move stuff over.

Cheap DRAM-less controllers usually wait until the drive is almost full to start folding. And then they'll only be folding just enough to free up some space. Most benchmark results are consistent with this behavior.