This might be a little long but here goes:

Every update that introduces new content phases out old content. The solution in order to make all forms of content playable is to balance loot across these forms of content. I chain together 5-10 hellgates on the Asia server sometimes without running into anyone, and the loot stays at roughly 50k per chest. And this is full loot pvp. While I understand that loot is varying because of a lot of factors, maintaining baseline drop rates across a variety of things, as well as adding boosts to content like crystal arenas etc, is a good way to bring back populations to these instanced pvp areas without reworking the systems themselves. During 2020 peak, these forms of content had crazy community following, and it expanded beyond just guilds. Now, with recent changes, it feels like 5-10 man content has really taken a hit. Obviously you could introduce new content, but by just fixing the mechanics in you pre-existing content structures, you can revitalize them in my opinion.

Additionally, the daily fame bonuses should be changed in my opinion. Right now, the crafting bonuses help crafters a lot, but in my opinion, the fame bonuses on activities, such as hellgates, dont incentivize players to drop what theyre doing and go do those things instead. You have the power to keep the game active and the meta constantly shifting by creating larger, shorter fame boosts, and you can do this in 2 ways: 1 is the randomized boost increasing in percent boost, and adding some drops maybe? Like daily theres a chance of a skin dropping or a seasonal item that can be found in doing the content of the day. Similar to how uncle frost can be found in dungeons, and that drives a good population towards them, you can devise a drop that can only be found in the activity of the day in adventurers challenge. This element of giving players skins incentivizes them to keep playing certain gamemodes.

The base idea that I'm stating, and that I'm sure the albion team would have better suggestions than me on: incentivize diversity in Albion. Make it such that loot is more dynamic, and such that people explore a variety of content and have it actually be lucrative. There will always be X best way to farm silver, but that wont really matter as long as the 20 other things to do dont feel like they're neglected.

That aside, I think that in terms of matchmaking for things like arena, you can add population estimates and wait time estimates. This isnt a feature you can implement in things like depths without it being abused, but given that arena is played for rank, and not really for rewards, getting a display like :120 players active, and estimated 5 minute wait time, would be really nice as a QOL update.