I am almost certain that both will be NHLers, but I think Lindberg is closer. SEL is a (slightly) better league than the AHL, and while Lindberg was a genuine star in the SEL, McIlrath was up and down in the AHL, often showing age and inexperience.
That said, I think Mac's potential is as a first pair defenseman similar to Beukeboom, while Lindberg's is a second line center. Not saying they necessarily will reach that, but that is their ceiling.
The idea that a 21-year-old who can dominate the SEL has only a third line potential is ridiculous.
Zuccarello did that at 22, and was far from ready when he first came over.