Offering perhaps deeper understanding. Weight of a tire does not affect MPG in the simplistic way that it's being presented here. Yes, it does, but as a far lesser secondary factor.
For tires of the same size...
Rolling resistance is the primary factor. That is a largely independent quality vs. weight.
Tires have to be designed from the outset for low rolling resistance. Rolling resistance is not affected by weight as much as it's being assumed here. It's within the fundamental architecture of the tire, which can be prioritized against other qualities. A tradeoff made for other aspects - tread pattern, tractive, and durability qualities etc. - some qualities of a good AT tire may be directly diametric to the qualities that make for a good low rolling resistance tire.
Some tire manufacturers will present the breakdown of qualities (with perhaps marketing tweaks), to help consumers understand what the tire model excels at or is biased for. There are AT tires that do better in regard to rolling resistance, i.e. fuel efficiency. But may give up qualities elsewhere to do so. It's really not much of a weight thing.
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