Discord is absolutely what has replaced forums and old social media. Twitter/Facebook/etc are entirely short form content and ragebait bots. Discord is where people are going to talk to their friends and discuss games/software/hobbies.

>there's a major gap in the market for an actual "social" network.

The problem is there is basically no money in it and it's hard build an engaged audience anymore because people attention spans are completely occupied by short form video and content creators now. Every minute of time people are willing to spend on their phones is currently used up so you are fighting against platforms that are much better at taking a slice of that pie.