I am not sure if this has been suggested before but a few things could be added to the PvE(-C) servers to spice the gameplay up a bit.
Clan wars/capture the flag: You could add a function where one leader/officer could formally “declare war” with another clan which enables pvp outside the pvp times or allows limited damage to thralls/pets during pvp times. You could also have points of interests on the map that would give certain cosmetic rewards such as specific weapons, outfits or dyes to slightly encourage the competitive aspect. I suggest cosmetic rewards because I understand that it should not be a game breaking aspect of the game which not all players will be able to access (solo players for example). In order to avoid exploiting or “taking turns” to unlock the cosmetic stuff, you could make these cosmetic rewards only available when the clan is in control over the point of interest for example. How the point of interest could work is an obelisk like structure which needs to be attuned to by one clan member and then protected for a certain amount of time to ensure control of the objective. Building would have to be prohibited within a certain vicinity or the buildings would be have to be destructible near the objective. A possible way to make these buildings destructible is to create a “clan war building category” which could be by default destructible.
Arena/Tournament System: There could be a tournament or arena system which could provide unique cosmetic rewards such as titles, outfits and weapons. For starters, a Leadership board could be implemented which rewards the top 3 players of the servers by the end of the week. This can be done in the PVE way where players would fight various NPCs in a 1 on 1 fight or even 1 vs many. As they fight more and more opponents they accumulate points which are added to their overall weekly score. I suggest a PVE layout because sadly pvp could encourage exploiting the system with conceding wins to each other.
I understand that these suggestion sound quite hard to implement but I’d be happy for any amount of content to be added to PVE (-C) Servers as the game does need some replayability as well as goals post level 60. To make this content last for a long time you could make the cosmetic rewards seasonal or monthly so there is a reason to redo the content. Any feedback to my suggestions is always welcome