I’m going to TL;DR; the TL;DR; post that I’m replying to.
- Fact: If your Delve level is lower, you will finish more quickly and more easily.
- Fact: If your Delve level is higher, you will have more renown but might not win the Delve.
- Opinion: It is smart to keep one faction very low-level so you can get Boss Room rewards without spending a lot of time and effort. This will quickly overpower renown rewards.
- Opinion: It is smart to keep all factions relatively low level until you are pushing the hoards very far. Having the ability to quickly clear a particular Delve and get boss room rewards will overpower the missing renown rewards.
- Opinion: It is smart to push all factions as far as possible to maximize renown rewards.
I think the third opinion, “push as far as possible”, only makes sense in the future when more renown is available. Right now you are potentially sacrificing guaranteed legendary ingots in return for 1 guaranteed common ingot if you maximize renown. I guarantee you by the end of the year, the +1 ingot reward will have given you less mythic ingots than you would get from a Boss Room chest by the end of the month.
The only reason it would be sensible to go “as far as possible” is if you are confident you can beat the Delve all the way up to 500. Then you get the renown bonus and the boss room bonuses. I don’t think anyone sane thinks they can reliably beat a level 500 Delve yet.
I think most people except the die-hard competitive players believe keeping at least one faction lower-level is the best approach. There are arguments to be made for and against holding all back, I think that one comes out in the wash.
I’m also not completely convinced yet the room multiplier boosts chest rewards. I’m trying to work out how I got 14 ingots from a 3.55 multiplier. Where is my math failing?