In a white room yea, but I would add the +5/-10 feats are way overated past around level 7 unless your DM lets you buy magic heavy weapons or purposely puts them around just for your characters and at high levels they need to be good magic heavy weapons if you want to keep up, and if a DM does this then they can be OP .... but it is an easy fix!
If you play most published campaigns for example, and don't buff them with extra items, there are only I think 5 magic heavy weapons total in all of the WOTC hard cover campaigns, with most having none at all. And of those only one is Legendary and it is sentient and evil. On the other hand magic daggers and magic staffs are ubiquoutous and they do more damage in the hands of a Monk than they do in any other PC.
When I was DMing and playing the 2014 rules I saw a lot of PCs using GWM and GWM-PAM. Often a Barbarian or a Fighter or a multiclass of those two and almost all of them were disappointed in high level play because when they attack they had the option of swinging their non-magic Glaive or something like a Flametongue Longsword or Staff of Striking.
Bottom line - the -5/+10 GWM great mathematically , but it is downright weak at high tier 2+ if your DM uses random magic items or published campaigns. Same with CBE. Sharpshooter is better though.