If you could make impovements to Deep dungeon...

[Felis]

No, instead people will get frustrated and quit. You can give something longevity in other ways than by RNG. Like making it fun and not just people button mashing mobs.

The dungeon is just poorly implemented in its current form.

Low droprates, low spawnrate or RNG. Choose your poison.

Longevity is about how many times you have to do a content. It can be fun, but it don't help if everyone get every reward within the first week.
So, ask for more puzzles, but not for less time sink.

[Zojha]

Longevity is about how many times you have to do a content.

And the relic works "wonders" in that regard without even needing to touch on RNG.

Fun fact on that note: If you have two progression systems, one with RNG and one without, both with the same amount of average effort required, only the RNG system can produce cases in which someone gets his things "instantly".