30% like rate on a paid TikTok ad is genuinely insane, most people are ecstatic if they hit 3-5%. your friend is right, thats not normal and you should treat this asset like gold.
the move here is to not touch the original video but build around it. since your goal is discord signups, you want to use this video as your awareness layer and retarget everyone who watched it (especially 75-100% viewers) with a second video that has an actual CTA pointing to the discord. TikTok's retargeting off video views is underrated and barely anyone uses it correctly. the warm audience you're building from that first video is going to convert at a way higher rate than cold traffic, so dont burn your budget trying to jam a CTA into something that's already working as a hook.
one thing i'd also test - duplicate the ad and add a text overlay or caption that mentions the discord without changing anything else about the video itself. sometimes that's enough to capture the people who were already interested but didn't know what to do next. keep the original running untouched as your control.
and seriously, reverse engineer why this video works before you make new creatives. 7 seconds, organic feel, clearly something about the hook or the content itself is clicking with that demographic. whatever that "thing" is needs to be in every piece of content you make going forward.