Ok prepare for some autism
hypothetically your frontline ships use 10 oil each, backline uses 7, as I posted, each clear give 100xp to all and frontline always have mvp
In 1:1, it's 200/17=11.76 xp/oil per clear. If you account 10 oil fee, it's 200*5/(17*5+10)=10.53 xp per run
In 3:1, it's 400/37=10.81 xp/oil per run. If you account 10 oil fee, it's 400*5/(37*5+10)=10.25 xp/oil per run. In the case where 3:1 is better, in this hypothesis, the backline of your 1:1 consumes 8 oil and over while your 3:1 still consumes 7. 3:1 is better if your backline in both case uses over 8 oil
If you are a real autist, here's the formula
(xp per bote)*20/(total oil usage +10)
Put your own number in and compare. Bigger result = better oil economy
The difference seems marginal, but remember, I only benchmark with 100xp. The more xp you gain per map, the greater the difference. Also oil usage of each ship is different, only xp is constant if you are on a specific map, so play around with your elite and rare botes if you can. You also get more boxes and equipment going 1:1. That said, I'd prefer 3:1 because it's faster and more consistent, and I don't have a repair boat.
In conclusion, 1:1 is better if you are a desperate oil autist. The drawback of 1:1 is time. But you can always auto it and do something else. 3:1 however is far more supreme in terms of consistency.