It's entirely possible that they were more intelligent in some ways than contemporary Homo Sapiens. How they were overwhelmed is open to question. Perhaps just numerically - they were adapted for cold environments and may have been less fecund.
If you assume that they're equally productive, sure. Why assume that?
Thru-hikers are often expecting to burn like 6000 calories a day.
Arctic explorers burned up to something like 10,000.
Would Neanderthals burn 30-50,000 calories in the same situation, or is that just "what Neanderthals did all day", as opposed to me, a guy sitting at a desk, burning 2000-2500 when I get my steps in?