Before anyone asks, yes, this is my first speedrun attempt.
I'm trying to work through a strategy for this from scratch, and I'm having issues figuring out which confidants I should focus on. Right now, here's what I have planned out. I was looking for some feedback on what I might be overlooking or putting too much importance on.
Remember, this doesn't factor in the auto-level confidants.
DEATH 10 (Healing Items are Super Nice)
PRIMARY PARTY (Goal being to get through as much of the game with only these characters):
Hierophant is basically pointless past rank 2. You want the basic coffee, and that's all you really need. You don't use SP often enough in the run due to avoiding all non-mandatory shadows essentially after the first palace to ever warrant ranking Sojiro past rank 2.
Temperance is pointless flat out. There are more than enough opportunities in the run to make more coffee than you'll ever need from Sojiro, to the point where you won't ever need anything from Kawakami. Same with crafting.
Hermit is pointless for the reason you gave. It's only actual benefit would be the mementos scan so you can skip the floors on the last section which is faster than going through the floors. However, the time it takes to actually get enough kindness (you need rank 4) to even properly start Futaba's confidant (which is a time waste simply to rank up as well) as well as actually rank Futaba herself means ranking her up period isn't viable.
Devil is preference, but pointless if you get competent at dodging shadows and knowing the places when you can/can't take alert.
Tower is basically pointless. Too much wasted time to rank, and the benefits simply are not worth it.
The main confidants you're gonna be wanting to rank are: Death (Tae, to rank 10),Mishima (rank 3) and Sun (to rank 10). We use Sun to recruit Girimehkala in Okumura's at a lower level and he is extremely useful for the run. Mishima is for the first exp boost, and Tae is self-explanatory; most broken thing in the game.
In the current WR route, what is ranked is
Ryuji (Rank 2, for Baton Pass)
We do pretty much most of what you said in your post: run past all shadows, do all palaces in as little time (usually 1 day) as possible, use very little SP items in battles outside of several occasions during the run mostly because there is no need to really and we still don't really ever need any of those confidants at any point to be safe in fights/palaces.