counterargument -- these people are making money off of transcribing other people's parts, with no profits shared with the composers.

No.

In some cases, the composer makes the video, and is sharing their own work.

In other cases, the transcribed part is not a composed part, and the composer who is listed (Lennon/McCartney) did not write or perform it (e.g. Ringo's drums).

In yet other cases, the composer was long dead before the recording was made, and the melody being transcribed is meaningfully different than the one they composed. Common in jazz.

"Composer" is a 19th century idea, enshrined in copyright law in the 1920's in order to protect the people who made sheet music for piano players to play in their parlor. Musical expression deserves attribution and protection, but let's not pretend the name on the liner notes is a Beethoven with a long quill creating a work of genius out of their solo effort.

That's a bad counterargument. Transcribing is transformative. Copying a video into a PDF is not.