Its doubtful that a clan made up of nearly entirely Rookie level players with just a few Pro level can maintain M3, especially if most aren't grinders. Tournaments have too many points available. Even if you only have 6-8 players playing Expert or Master, if they are decent, they can put up a ton of points quickly. Without me putting up 10k, losing a few 1k+ players and about half team not playing there's no doubt we're not going to make it to M3 and depending on the upcoming tournament may fall back to M1. So when you're looking for a clan to go to M3, definitely make sure they have some Expert/Master level players in tournaments because otherwise the entire team needs to be grinding out around 1k+ with a few big grinders getting 4k+.
My other clan doesn't grind at all, its almost all tournaments and we won M1 probably by double the next team, and currently in 3rd in M2 because we had a terrible tournament and only put up about 20k in the last tournament. If we have a good tournament though, we can easily jump up to 1st and we're not even trying to make a push because most of those people have other accounts in Clannibals who are fighting for 3rd in C100. Tournaments are where its at and rookie/pro level tournaments are a waste of time unless you finish Top 3 in rookie or Top 10 in Pro.