Another pro feature is realtime collaboration: " Enterprise Edition -- Provides a commercial version for enterprises with specific needs, including but not limited to multi-person collaborative editing and browsing, data connectors, and Live Share for collaborative browsing."

Lost me at Sheets Import/Export (Pro Feature)

Open source .... but who would actually use it without the 'pro features'?

Forking seems to be a sufficient value of open source.

Perhaps hou just mean, how do they expect traction if the open components dont entice marginal users

Only a pro needs to export Sheets.