Amethyst is a power house when it comes to connecting to relays. Primal's backend collects what it can find and serves it to you from a caching server. There is some difference between the two, in what is considered a like, as well, so that creates even more of a gap sometimes. Primal is almost more of its own little ecosystem, like a house with of big glass windows.

You're probably right about who sees what and from where, being possibly different. I've noticed that increasing lately, too. Growing pains. More relays, more clients, more ways of handling data, etc.