Actually, after the sixth hit, you'd just go to the right below the blue platforms, thunderbird will descend absurdly quickly and since you only need two hits..
Comparision with dood's WR https://streamable.com/222u3u already near-simultaneous and not as mashy as it looks. In fact I don't remember mashing like, HARD, for this.
Since there's no RNG for at least the starter of this fight you can copy exactly what I do and it'll work. The key is holding down the down arrow key while mashing.
- if I had been facing the other direction here(circled in red on the right) that in theory would have been the two hits needed to get an insanely fast boss clear here.
Start using this. Preferably with finger cam / input display to make it easier for other people to learn and for me to continue doing. I would have done so myself but I didn't really expect this to happen.