It has generally been true that due to historic typical use applications and manufacture typical USB drives were better than typical microSD for boot/system disks. But there is nothing inherently better about the memory in USB drives. If we are comparing to industrial SD cards above (whether MLC with wear levelling/ECC or SLC/pSLC type) these may be better than many consumer USB drives and even as good as some SATA/NVME SSD drives.
If you are having to buy another (USB flash) drive, why not spend the same amount of money to get a much better quality microSD and also not have to bother with the extra configuration involved? I think this warrants serious consideration now that SLC and more robust MLC/pSLC microSD are much cheaper than they used to be.