Relevant discussion about channels to support, channels to keep updated (and therefore channels to not support nor keep updated 
): Are there other channels that you would prefer to use in addition to or instead of this forum for Movement Strategy updates and feedback? Why?
From the three points you make, critical mass of users is the deal or break, and the one that we all have more possibilities to act upon.
The other two are more related to business and tech (tightly related). Discourse cannot compete with the budget and tech of Google, Facebook, etc. But the desktop and mobile user experience is good, Wikimedia login helps, and here nobody is tracking you and selling your private data (the only reason why those companies can be among the most profitable in human history while users don’t pay a cent for their services).