Ugh, this thread frustrates me as the guy that laid out how to change themes to begin with, and even initially received a similar soft brick myself, but was able to fix it thanks to having a coldboot CFW that could bring me to the homebrew menu and then FTP without touching the point where the Wii U would freeze at the logo. But I also explained exactly how to fix that issue in that very first post that explained how to do all this theme stuff to begin with, that explained the process I went through. All you had to do was try again in FTP until it properly copied over, it could take many tries, but was easy enough to check by simply exiting and re-entering the folder you're copying to in FTP until you see the file size in the Wii U is the same as the copy on your computer you're trying to copy over.
THIS scenario, is a shining example of why these kinds of video guides are bad, I did not commission or recommend that video, and the person that put it together did not go into detail in how to fix the soft brick that can occur. So you, the user, freak out and try to solve it without the guidance I had provided from the start and only made it worse. Having said that, unless you bricked your Wii U too far with your attempts to save it on your own, you should still be able to save it.