That's a bummer to hear; I have the WD15 dock through work and it's been excellent; I have a bunch of complaints about the XPS itself (power management, for example), but that dock has been great.
For the prices, these docks have no excuse for bad behavior.
I dunno, TB is basically a mass of high frequency analog madness with long cables thrown into the mix. I, kind of astonished that it works at all, at any price.
I also have a WD15 and it works very well. Connecting everything with one cable is a very nice feature. It's a USB-C dock though, and not Thunderbolt.
I have the WD15 connected to a 2016 MacBook Pro and it is incredibly unreliable. USB devices stop working randomly (mouse+keyboard), ethernet comes and goes as it pleases and the display output works for one month before stops working all together. The only thing that works reliably is power supply.