QLC has lower write speeds hence the lower than stellar figure. It's still significantly faster than HDDs because while HDD RAID(or similar) Arrays have significant performance improvements, they will do the same with SSDs. So the lower write speed is less of an issue.
The biggest concern for a data center environment I would assume comes down to longevity. QLC has lower write speeds but also lower lifetime cycles. Depending on use case it may be cost prohibitive to switch to an all SSD rack.