I'm not so sure it's an issue of TLC/QLC memory at all.
It's that to make cheap drives, costs must be cut and this can be the outcome: bad write performance.
With a TLC-configured controller each write is actually three consecutive program/erase operations on the affected NAND cell. With QLC it's four such operations. All MLC schemes - DLC, TLC and QLC - are cost-cutting measures, and the technique inherently incurs a performance and endurance toll.
I know and understand this. However there are plenty of well-performing TLC drives at higher price points, so it doesn’t seem specific to TLC memory, there are other factors at play I think.
Larger drives are faster because in order to provide more storage they have to use multiple NAND chips, which the controller interfaces with in parallel. Older DLC SSDs of 250-500 GB could often sustain e.g. 550 MB/sec write speed (SATA-III bus maximum) indefinitely, but most 120 GB models from the past few years use a single NAND chip, and as of late this is also the case with most 250 GB models. The idea that the cheaper drives are slower because of some unspecified generic cost-cutting is a fallacy. They're primarily slower because of iterative MLC exploitation and because NAND-cells-per-chip is growing.
