Prior art still invalidates patents in first-to-file systems.

First to file only means that, if you filed for a patent on some thing after someone else who also filed to patent it, you definitely don't get the patent (in a first-to-invent system, whichever of you can show the oldest documentation of invention gets the patent).

Under a first to file system, you still have to be an inventor. If you're trying to patent something that you copied from someone else, you're not an inventor.

And even if you didn't derive your work from theirs, you still have a problem with prior art.

First to file doesn't mean anything if there's prior art.