AI foom is said to happen if at some point in the future while humans are still mostly in charge [...]

Humans being in charge doesn't seem central to foom. Like, physically these are wholly unrelated things.

mechanisms like recursive self-improvement can only cause foom if they come earlier than widespread automation from pre-superintelligent systems

Only on the humans-not-in-charge technicality introduced in this definition of foom. Something else being in charge doesn't change what physically happens as a result of recursive self-improvement.

essentially removing humans from the picture before humans ever need to solve the problem of controlling an AI foom

This doesn't make the problem of controlling an AI foom go away. The non-foomy systems in charge of the world would still need to solve it.