I don't think -5/+10 is overpowered it's a (not-so) high risk vs high reward that help value martial against spellcaster, which have potentially high damage or usefulness. It's not AoE damage but single target one too so it's not an "i win" button. But it's definitly strong and it's the whole intention behind it - to increase the lethality of those weapon use.
It's that some of us want and expect feats to cater equally to all martials regardless of your choice of weapons combo.
That is the real downfall of the -5/+10 feats. It's essentially saying this:
§1 if you play in a combat-heavy game, your primary job as a character with a weapon is to defeat monsters
§2 the primary means of doing that is to
cause damage
§3 if you want to do your job well, you need to drop that parrying dagger, you need to drop the flourishing cape, you need to drop the shield...
...because
§4 greatweapons and ranged weapons are
the only two tools that get the job done right
That is the first and foremost complaint.
Not that you deal more damage in general. Not even that you deal much more damage compared to non-weapon users.
But that ALL weapon users will be compelled to choose either greatweapons or ranged.
It is boring. It is unfun. It is limiting.
It is all of the things opting for feats
should not be.
---
Compare to a different game where the feats did not simply increase your damage output, but actually enabled you to pull off special stunts you could not otherwise do.
That is: not taking the feat would still be an option. Taking ANOTHER feat would still be an option.
Many other feats clear this threshold. The cleave part of GWM is powerful, but not so that it completely overwhelms the alternatives. Sentinel, Polearm Mastery, Mobility... there are several feats that I would consider good design.
The -5+10 feats does not belong in that group.
Those feats require you to first agree to the assumption "dealing damage isn't very important", and in a combat-centric game that is just not true.