Arguello relied a ton on working from the straight line. Loma relied on getting off it to attack. Same reason Pryor was horrible for Arguello, but Loma has better defense and better fundamentals if not the chin. Loma has looked pretty fantastic when he chooses to agressively pressure and doesn't need surgery. I'm not saying he smokes Arguello, but that is a close fight due to styles. Think Harada/Jofre.
Pyror was horrible for Arguello because Alexis was a past prime former featherweight champ fighting a prime, full fledged junior welterweight champ.. Alexis still gave him all he could handle. Lomachenko is past his bet at lightweight, can't hurt Arguello like Pryor could, and is simply not as good as Pryor in any case.
Loma would be scared to throw a meaningful punch for 6-7 rounds and when he did, Arguello would knock him clean out. Then Loma fanboys would claim an injury.
In comparisons with great fighters from years past I always come back to this. You don't have to be a legend to land on Loma so for me the question becomes is Loma possessed of an ATG chin and recuperative powers? If he gets beat on for most of a round by Mexicutioner-era Manny Pacquiao (for example) is he gonna stand up to it? To date he hasn't fought anybody of that caliber.
Loma is an extremely talented fighter. He possesses all the tools, maybe except the power in the higher weights. I always go back to a simple question. Who has Loma beaten that makes me believe he would beat a prime Arguello. The answer is nobody. Then I ask, how would Arguello do against Loma's opponents. IMO, Arguello doesn't lose to Salido, or have any problems, even if Salido fouled all fight long. I see Arguello giving Teo a comprehensive beating.