"TikTok is vape and Reels are cigarettes".
TikTok's algorithm is _super_ curated and targeted, like a Mr. Beast video. Instagram's is pretty good but if you can get your algorithm to the brainrot cluster with everyone else then you'll get a lot of out-of-left-field, grungier content you might not find on TikTok.
I think once RedNote gets banned or the meme fades people will mainly flock to IG. There's still a void of creator based features that IG can't fill, so maybe a competitor will pop up if IG can't replicate the environment well enough.