Well that’s about to change.
Dell XPS 13 has GREAT Linux support in fact, they sell a version of the XPS 13 with Ubuntu Linux pre-installed.
I think you should try out some distros in a virtual machine first so that you can try out the interfaces rather than going through the process of setting up persistence only to find out you don’t like that setup.
Virtualbox.org for the VMs and then you can just download the ISOs from the particular distros.
Once you find the distro you like the best as far as user interface then you can move to the USB thumbdrive approach with persistence if you want.
Zorin is good but it is rather limited as well. If you would like to try it out then I suggest that be one of the systems that you test in a virtual machine approach.
I would also suggest the following options to try:
These all use a Windows paradigm interface so you should be comfortable with any of the 3 above or Zorin as the interface will be somewhat familiar. It still wont be Windows of course you there will be a slight learning curve even with the similar interface.
USB drives are flash based so they can have similar speeds to SSDs, provided the quality of the drive is high end.
It can also be the USB drive that you used. They are not all created equally. I have had some very nice high speed drives from Sandisk and some others that calling them sluggish would be kind.