If you want your guild to go further in the GE, then it's better to institute a mandatory weekly minimum # of encounters that everyone needs to complete. (ie: a typical 'casual' guild will on average ask for everyone to complete 12-16 encounters/week)
...on the other hand, a typical 'competitive' GE guild will mandate ALL members *must* complete at least 32/48, if not 48/48 as an absolute minimum. (and obviously mandate full Lv4 completion on 'challenge' weeks vs. one or more similarly competitive GE guilds)
rankings in the GE are simply which guild/s are the first to get ALL members to complete 64/48 encounters, up to a maximum total of 133.3%
The pts per encounter are based entirely on the age of each individual player and as mentioned above, go towards your Guild experience & leveling up your guild.
(higher age players naturally earn far more pts/encounter vs. the lower age players)
If your guild struggles to average even 10-20% completion each week, then it's probably a better idea to find a better guild!