$27B and $8B AUM are both peanuts, and I imagine not a big factor in determining valuation for these robo-advisors. Corporations are likely more interested in the number of users, demographic breakdown (mostly well-off millennials), their financial data, credit profiles and upsell opportunities.
This. The amount of money they manage is a mouse fart in a hurricane when it comes to such low fee business as robo advisory. That a robo advisor can get $5bln valuation on having $8 bln of assets speaks either to the silliness of the valuation or that the value is not in the assets managed (likely a combination of both factors).