Microsoft Exchange is not entirely compatible with normal protocols in subtle ways to provide outlook-only features which makes it very difficult for me to use my preferred email client for my work emails. So I am naturally forced to use outllook while I hate it.
Gmail can easily mark any small and private email domain as spam making. And in fact there are many stories like these, where people stopped self hosting their email server to use a bigger player (and often pay for it) so their emails are seen. If gmail was smaller, they wouldn’t have so much power as forcing most people to not host email.
So the conclusion for me is not corporate vs free/FOSS. But more about preventing having too much power in a single instance which is why it is important not to let threads federate and take >90% of the content, participants, etc…