CapnZapp
Legend
Okay I'm at my computer now... but I really don't know what to say. "Cool character, bro" perhaps?Well then, let's post some tables.
SCENARIO: Level 11 barbarian with a +2 great axe. With the feat, his strength will be 18. Without, it will be 20, so there is an opportunity cost to taking the feat. This is not a "Made up" example. This is an actual character used in play (Lal Qualandar, in the Al Qadim game that [MENTION=20323]Quickleaf[/MENTION] is running).
please stand by as I find a way to post the table.
View attachment 87078
edit: I believe it should be now visible in jpg mode. Please note that the table doesn't take into account critical hits. I readily admit that there is no "turn a near miss into a hit!" feature, but I'll also note that there is no easy way for this character to actually achieve this - he is not a battle master and there is no bard in the party either.
I'm afraid that if you want to make a case that GWM isn't "all that", you need to create a character that uses the feat in an optimal way (or close to it, anyway), yet derives not so much benefit that we can call the feat overpowered.
The argument isn't "the feat is overpowered to Greenhorn Sue or Average Joe", after all. The argument is that "for a player knowing what he's doing, the -5/+10 mechanism is too abusable, too strong. Since there aren't any alternate means to similar amounts of damage, this leads to every damage-focussed martial PC looking the same, which reduces variability and choice. The feat needs to be removed."
Feel free to make a new attempt where the character we're trying to study is a Battlemaster Fighter with the Precision Maneuver (and the Lucky and GWM feats) and that the monster has Fairie Fire applied to it*.
*) you could equally well say the monster is prone, or that it his monk-stunned, or anything else granting us advantage really
As for the monster's AC, let's begin at a soft AC 15. We can easily redo the calculations at AC 18 later. We won't assume any magical bonuses at this point.