As much as it may hurt you guys to do, you need to take a stand & be just as inactive IMHO.
If the devs won’t remove your gl & all they’re doing is logging in & getting the rewards you’ve worked for - then stop. Dont do any tasks, I don’t know if you’re in gw or not which then presents an issue if you don’t do the gw battles, but just don’t contribute to the tasks.
While someone is getting something for nothing they’ll carry on doing so until they’re forced to act.
Your only other option is to find another guild & leave your gl by themselves - there are always plenty of spaces in guilds at every level of the game