Thanks for trying Phil. And definitely thanks to westfw for adding the issue and recognizing that Adafruit hasn't picked up on the change.
Personally, I think it is better to deal with the problem by implementing some sort of check, such as availableForWrite, rather than hide the problem in larger buffers,
As westfw was saying The Serial1.availableForWrite() on my Adafruit feather m0 always returns 1 byte, this is pretty ridiculous considering I bought it for the 32KB RAM.
Thanks again!