I've used Meshtastic as small (5000-ish person) festivals, and even with higher bandwidth settings and stock rubber ducky antennas, ground to ground ranges through trees and people of around 1km worked just fine (with the expected shadows behind hills). This was only a small number of devices, I have no idea how badly performance would drop off if 10% or 50% of the attendees were trying to tx/rx Meshtastic or LoRaWAN signals.
LoRa is designed to handle hundreds of devices in the same area since the commercial use case is densely deployed nodes. The spreading factor is orthogonal so it is able to multiplex in the same frequency assuming your data rate is constrained enough for the largest spread factor.
There's a bit more on involved with gateways and coordination that you don't get in P2P mode but the PHY has the pieces you need I'd you wanted to do something similar.
