I beg to differ and so would our over 1000 customers, none of them with less than 100 seats (we don't sell below that). Most have 1000 users or more.

The largest has several tens of millions of users and they are using Global Scale. One customer runs nearly 4 million users on a single cluster.

Nextcloud is a complicated beast, and scaling to tens of thousands of users isn't trivial, but then that is what Nextcloud Enterprise is for. So if you need a large scale installation, no problem - contact our team and we get you up and running.