Maybe I'm outvoted, but I'd say the 1.21 pack is not as good. It's missing some good mods like Botania and Create, and the main addition it seems to have is minecolonies - which doesn't work properly on other Craftersland servers anyway, apparently the townsfolk get deleted by the weekly reset. Can anyone see any other cool mods in this pack?
I think the main reason for the low number of players in the 1.20 server was the technical difficulties that plagued the server for the first few months. By the time most ppl could get into the server, other servers with this pack had been running for months. This might be an argument for switching to the new pack - to stay ahead of the game, if the server can be released without the bugs. I guess it's a question of what will attract more players.