[X] Side with Dorri and mop up the foraging bands
I worry that whilst we're mopping up the foragers, the elite warriors will be doing something too, maybe striking out in a group to attack Asvir, or launching a counter-attack and catching us whilst we're strung out from hitting multiple raiding parties. But ultimately it's usually not a good idea divide forces in the face of a superior opponent, and the opportunity to defeat our enemy in detail is too good to pass up on. Perhaps more importantly, allowing the foraging parties to run wild means any victory will be kind of a pyrrhic one, given our primary objective is to stop our farms from being burnt and families being killed.
If we had a castle we could send all our noncombatants to and which could hold off any raiders, then Logi's plan would be the best one. But short of that, I think Dorri's plan does the best at recognising our constraints whilst allowing us to make the best of a tough situation.
By what Solrun said, I highly doubt this would even help. Blackhand still had aging issues despite all his Odr after all. If it did help, it would do so via Hugr Infusion. And Steinarr infusing Hugr results in him going berserk. There might theoretically be a safe way to do it, but definitely not one we have time for.
Also, Solrun already offered a treatment. At least in the short term.
Also, Odr cultivation isn't like a Super Saiyan transformation or becoming an Exalted. There's not a massive immediate power-boost or physical transformation, it's more that it opens the door towards accumulating a new kind of power and doing things you can't otherwise, and that requires a lot of time and concentration. Something someone suffering from cognitive decline likely caused by a terminal illness has neither of.
Also Also: Ymir is our enemy, and is kind of dick. There is absolutely zero reason to believe it would balk at a chance to kill us just because Steinarr is nearing death or suffering cognitive decline. Indeed, the fact that Steinarr is not at 100% gives it a better chance of killing us and eliminating one more potential problem down the line. To assume the Enemy would not send a full retaliation is inviting calamity.