To say that the success of discord was due to "pouring VC money into marketing" completely misses the whole "we also spent a lot of time and effort to build a product that was better than what was out there and solved a problem for our users."
This is incredibly reductive. You don't use it because "you don't have a choice", you use it because it's the best. If there was another option out there people would use it. There are plenty of choices out there; you go set up a self-hosted phpBB forum; try to maintain a live community on there; and moderate it. Or forget phpBB, try Discourse.
When you say Discord is "Style over substance" you willfully ignore all the downsides about forums that caused people to migrate to Discord/Slack in the first place. We will never have robust forum software as long as people continue to believe that the reason Discord is as popular is it is is because of "VC marketing dollars".
Not always. I hate discord with a passion because I don't want to be data mined by some corporate walled garden. Unfortunately some open source projects have taken the decision to use it so I have to in order to communicate with them. Home Assistant being the most notable one for me.
It's a really poor choice for this IMO, matrix is so much better and you can use any client you want.
Discord's biggest advantage in my eyes is that it makes it easy to build a critical mass of users. This makes it easy for newcomers to get answers to questions quickly.
So your disdain for discord has nothing to do with user experience, ease of use, UI, or anything else someone might consider when actually using the product, but it has to do with the ethics of the hosting company.
I can say I hate Porsche because they benefitted from Nazi regime and I will never drive one for that reason, but I'm not going to try to assert that the Ford Pinto is a better car than the 911.
But Porsche's history is just that, history. If a Porsche 911 would send all my data to Porsche it would not be a very good car in my eyes.
I don't think the UI of Matrix is meaningfully different than the one from Discord though. It's a bit like clothing IMO. Mainstream users are very brand-sensitive. They buy Nike shoes not because they're good quality but because it says Nike on them. I bet it works the same way with services.
This statement seems to not account for lock-in or network effects. Why do people still use Oracle products or Microsoft products like Outlook or Excel? It's certainly a big stretch to say that these things are "the best" (although Excel is, objectively, the best) unless your definition of "the best" is simply "the thing we are currently using because if there were something better we'd be using that." This seems a bit circular to me.
Why do people use Discord (or Slack) for housing information instead of bringing it into a self-hosted forum or internal database? Because people were lazy when they started and they're too lazy to port it over now and the massive inefficiencies are distributed over time and a number of users. It's a tragedy of the commons.
Some of these communities are older than Discord but somehow they were lazy. It simply can't be because Discord/Slack are better tools. The implication that there are communities working on database internals using Discord, but they are too dumb to standup Discourse is astounding.
Another example: I used to use a wristwatch rather than my phone's clock (this is pre-smart watch) even though just using my phone would have been more efficient. Why did I do this? Because of habitual lock-in. How did I break out of it? I eventually realized how expensive it was to maintain my watch and that there was another option that I already had that did everything my watch did. In your world and under your definition of "the best" then my wristwatch was "the best" solution for telling time despite it obviously not being the most economical or efficient. Until it wasn't, and then my phone somehow became "the best" tool for telling time in your world.
Discord basically won because of style over substance. I use it plenty because I don't have a choice. But there's nothing actually good about it besides the VC money they poured into going to market and branding.