I disagree fundamentally with Steel path being the most optimal way to play. because Optimization requires inclusion of one's personal circumstances.
I have a borderline Solo Clan: I have to input 2 of each Curse, I have a week to get a total of 6 curses.
I'm Still ranking up the Syndicate (or getting all the things from the syndicate shop)
During Angels, Ranking up that syndicate during the same time, Doing it on steel path didn't really make sense, because you could do both at the same time. And I was able to buy the arcane rather than beat my head against the higher difficulty while you may have been done in half a month, and it took me 2 months. I'd argue I spent significantly less time on it because I was averaging 10 arcane an hour of playtime because I was maxing out rep... and then stopped playing that area.
During the Voruna update I actually agreed with you doing high level survival, with higher drops and higher chance of getting the rare stuff in a set timeframe just seemed to make the most sense here.
Citrine? You could rank up weapons while doing it.... So why go steel path when you can progress at twice the pace, So I was able to rank up all of my weapons and max them out with 3-4 forma during this. There was no reason for me to go steel path because I was getting crystals while ranking up weapons.
The most efficiently way to do whispers for me without even thinking about it, is Do the missions from fish that are assassination missions. You get rep, and you get a single curse. after you have 2 of each... you do whatever mission gets you the best rewards for your time. I have all the other stuff that I already farmed entirely during scarlet spear. so that's not a motivating factor at all... and I was able to get all but one of the Items during the first (half) week. The only thing I'm using my grotesques on now is Arcane energize. to melt down and buy the arbitration arcanes, because I'm not farming that I already have everything I need, and the arcanes there are stupidly low drop chance. I get other arcanes while I'm involved in other pursuits... So there's laterally no reason for me to play steel path unless my goal was to stop playing the game, and it's not.