Alrighty, so I did a little comparison video of The PS5 and PS4 versions of the game running on PS5, the PS5 version running at the "performance" mode. Thankfully Balmung's main city hubs are always crowded so it gives a pretty clear indication that the PS5 REALLY starts to get chuggy when there's a lot of models on screen all at once.

https://youtu.be/PVh2Z3Zg9PY

Also I know it's not like super precise science, but the clips were all captured within the same 10 minute period so they're consistent with player congestion.