My 3-year old A-Data Professional PD7-200x 8 GB USB pen drive still beats almost all other USB pen drives available today, presumably partly because it was based on SLC flash memory.
In those 3 years, USB pen drives have got cheaper, larger, and a little bit faster on reading; there has however been little apparent improvement in write speeds.
I'm guessing that this is largely due to the fact, that marketing specs for USB pen drives always include capacity, sometimes include read speed, almost never includes write speed for large writes, and never ever ever includes write speed for small writes. So there's no immediate gain for the producers in making USB pen drives that have better write performance.
Eventually, sometime, when technological evolution of flash chips makes it inevitable, we will see USB pen drives with faster write speeds, but the last few years have been disappointing in that respect.