I myself have run many +10 clans, and my intention was, even on PvE, have a bigger clan, maybe not 30+, but definately more than 10 players.
I think they have done it, since they expected to raise the max players from 40 to 70 I think, and that, I think, wont happen. So they had to decrease clan size, or it would be a first to come first to win, given official pvp servers will have raiding times.
For me, they should raise it to 15 minimum, even on PvE servers, because with higher clan sizes, we could afford having some semi casual members, test members, recruit noobs etc, but with only 10, that wont happen. I usually have some people that play often, and many that play sometimes, with big clan size theres always somebody around even if most of players are very casual. With 10 that’s…difficult XD