The devil on my shoulder says:
This is written on the box. You knew it when you did it and did it anyway. It’s been part of the argument, since Delve released, that one should keep levels low because it makes it easier to keep ingots, and only chase the 25% of 1 stat point maxing faction renown gives you when you never want to do a Delve again, otherwise you’ll always never want to do a Delve again. All scaling events provide a path of no return. So don’t advance if you don’t want to.
The angel on my shoulder says:
Honestly I don’t like the design decision that makes progress a one-way street and wish you could lower your Delve level. It should be expensive, so people don’t rush for maximum score then cheese the Delve back lower.
One problem is if you can actually lower the level, you get to exploit the multiplier. If I do level 20, then level 30, then level 20, then level 30, I got the 2x multiplier twice off of 30. So for lowering a level to discourage this, you’d have to start with a multiplier lower than 0.5x, preferably 0x. It should probably only let you reduce the level 10 at a time, otherwise jerks like me would loop 0-100 and still cheese it.
But I do think it would be fair to make it tedious and/or expensive to lower the level. Even if I do think the people who pushed it too high had clear warnings and didn’t listen to the community.