Probably most Guilds within the TOP50 could do most of the Boss quest without gems, with a good schedule and committed members you come far for sure. TOP100 and lower guilds probably needed their gems in lv.24 and higher, this because their force attack is just not high enough!
In the lower rank guilds many players have stats of 300K ~ 1 mill., therefore their force attack is between 800K up to 4 mill., simply calculation shows how far these guilds could come without gem use and max. commitment of their members. I think in many guilds most of the time only 75% can be simultaneously online, some are at work, some are sleeping etc..