1. Make sure they live & breath the company
2. Keep challenging them
3. Transparency as much as possible
4. Make them be part of the decision making process in the company
I think that by the end of the day this is a habitual battle.
The functionality is pretty similar and switching between messaging apps is like switching from Google to Bing => not an easy thing at all. Their real chance is by making a more engaging platform, and this is a real challenge as the offerings are very similar.
The technical validation is being done at the architecture level usually, and the due diligence is usually focused on the background and tech skills of the entrepreneurs.