While I agree with many of the points that have been raised, I think GWM is being sold short, mainly because they are being compared in a vacuum.

Even accounting that XBE and SS remove two of the most glaring drawbacks of ranged combat, there's still the fact that throughout the rest of the game melee get much more support than ranged.

You can't do AoO with ranged weapons. PAM/Sentinel will let you do it realiably.

More class features/spells that work with melee only (Divine Smite, BB, GFB among the most notable ones)

There's far more magic weapons compatible with GWM than with SS in the DGM.