I’m pretty sure your wiring is incorrect, or the resistor value is wrong for 3.3v.
You were right in more ways than one. After some digging it seems like I would be fairly content using the Axoloti RX pin (I'm only transmitting MIDI to the Axoloti) and programming the code using the fortyseveneffects MIDI library. The only MIDI messages I've gotten the Axo to receive are from this code:
I'm trying to put a pot in this code but it's not showing up in the Axoloti, but that's probably because I've written the program wrong. I'm really that new to programming
Finding a way to make the Axo read usbMIDI would be a huge boon as well, so that project continues. I mean, is Teensy the only MIDI-compliant device that puts serial before MIDI messages over USB? What's the difference between a manufactured USB controller (like my Launchkey) that works immediately when plugged in vs. the Teensy? Also, is this a problem for Arduino UNO users?