The biggest disappointment with the current version of relics is just the complete lack of satisfaction once finished.
When you finished a relic from previous expansions, you at least felt something. Now, I can get the tomes I need for an upgrade at the same time as I just get my weekly tomes capped.
I literally don't have to change a single thing in how I play and I get a relic. That's boring AF and doesn't make me want to even do it. I mean I have 15 of the newest upgrade item just sitting in my inventory. And I have weapons to upgrade. I just don't care.

As for why relics are good to combine with other content? Grinds are boring by nature. If you combine 2 grinds, it gives way more of an incentive to actually do it.