When we're talking about a fairly underwhelming pro like Campbell, it's notable to point out that Lomachenko had some issues with him, especially when Campbell makes up 1/4 of his LW career. We are talking about Lomachenko being a very big favourite over two of the best LWs of the last 30 years, so it's important to establish what he has and hasn't done at the weight, no?
A guy like Marquez has fought a laundry list of elite fighters, several above LW, and has only been clearly beaten once in his career, by a bigger, prime Floyd Mayweather. For a LW to be considered a strong favourite over him, I expect for them to have showcased something very impressive at LW, or possess, in abundance, the abilities that have previously troubled Marquez. Lomachenko certainly doesn't have the performances at LW that alone merit him being the clear favourite, so one would have to blown away by his skillset and how it particularly fits against Marquez. He doesn't necessarily have all the tools which have historically troubled Marquez. Lomachenko has great feet, but he's not necessarily a guy who moves a ton on the backfoot and forces a guy to chase him, or fights behind a commanding, strong jab. I don't really see much which would lead to me to strongly favour Lomachenko in such a fight.
What I do see is a highly competitive fight with tons of question marks (mostly because Lomachenko doesn't have much to go off of against elite competition). There is very little we don't know about Marquez, but tons that we don't about Lomachenko.
Also, who are "you guys" and about what are we "usually wildly off"?