OP here, I updated the CLI input and even made it a script you can save and launch as a file. I don't really notice any quality improvements doing this vs saving from the webp file but idk, this is more "correct" I guess?

for %%f in (*.png) do (
ffmpeg -framerate 1 -stream_loop 1 -i "%%f" -c:v libvpx-vp9 -quality best -crf 10 -qmin 10 -qmax 10 -pix_fmt yuv420p "%%~nf.webm"
)