.. yes, there are companies that rely on other marketplaces or apps, though I am not able to quote any serious businesses in Europe or USA that does this - all the businesses I know tend to get their customers off the platforms they don't control to their own websites and CRMs.. only small-medium businesses seem the ones that place trust in various apps and marketplaces..
domain investors are different, though - in general, most (small-to-large) seem to rely on marketplaces.. with few exceptions, like Mike Mann
For Domain Summit - I am slowly getting prepared for a step when we will develop our own (self-hosted) solution where we control the data 100% - probably will start development 2nd part next year.
this is what totally confused me in Hong Kong - seeing how businesses trust WeChat over growing and controling their community on their own platforms.. very very strange - and an economic suicide if WeChat closes your account for some violations.. and, there is a saying that came out from the old Soviet times: as long there is a person - we will find him a case (criminal case)..