I agree with this, for good Minesweeper players (my record on expert is around 55 seconds) a rate limit of 3 per second is low enough that it feels frustrating and glitchy. I think I averaged approximately 5 clicks/second on vanilla Minesweeper, but presumably with higher peaks. I imagine at launch you're getting more curious first-time players, but your community would likely gravitate towards more experienced players over time.

A simple suggestion to encourage more fair matchmaking without building a big system for it is to have separate Beginner, Intermediate, and Advanced boards, and let players self-select.