The ownership stake is dependent on how the negotiations go and how much the company is looking to raise at what valuation/terms. Social Capital will argue a liquidity premium should be applied, and I'm sure the company will say what you're saying (they can IPO <1%). However, they could both stand to benefit, so I see a deal happening with this SPAC
I do think you do raise a fair question of what stake Chamath et. al should get for sourcing a deal. 20% is definitely high, and I think a typical SPAC is something like 5% sourcing stake for the owners.
20% is standard SPAC comp.
Also yes, I apologize, you are right - they get 20% of the value of the SPAC, so if they buy 10% of a company, they are only getting 20% promote on that 10%.