I was going to make this same objection. Your assertion that level 2 tasks are multiplicative with each other is not very plausible. It's obviously false that each typing class improves the typer's ability by 20%, since I can't take 10 typing classes and start typing at 400 words per minute. More likely the gains with multiple typing classes are linear for the first few, and sublinear in the long run.

It is more plausible that level 2 tasks are multiplicative with level 1 tasks. If you get 20% faster at typing, you can transcribe audio 20% faster, and every level 1 transcription task you undertake now pays 20% better.