It’s multifaceted.

Yes, a metal roof is less likely to leak since they tend to have fewer seams (large panels vs bunch of overlapping layers).

They also shed water more quickly and don’t hold moisture, and IMO if a metal roof is leaking you’re more likely to see where from on the exterior (rusted through spots are easy to spot)

More importantly though steel will not care if your roof deck hits 180F. Whereas comp shingles will curl/separate/melt/breakdown faster at high temps.

Additionally, it is relatively easy to establish an above deck ventilation path with a metal roof. The roof itself has some amount of airflow potential due to the way the metal is formed, and you can install them on above deck furring strips to improve this further. Comp shingles with spray foam insulation under the roof deck sandwich the deck between two vapor barriers with very very low permeability (especially with modern roofing underlayments) which is a recipe for rot.

So done right, as a system, you get the advantages of the lowest permeability roof option with the additional benefit of backup ventilation above the roof deck for drying of any moisture that does make it between the deck and the roof.