Two follow up questions: what would you consider poor damage?
I struggle with the gish because it seems that to be an effective warrior a lot of your magical resources have to be focused on that, meaning that a lot of the flexibility and utility of being a caster can be lost. If you go for high utility however, you can end up being mediocre at everything
A class with a single attack (maybe 2) that has no class feature to boost that damage. Example Druid, Valor Bard.
Fighters for example get action surge+ a weapon style so even a longsword+duelist style is dealing what I consider moderate damage. high damage is something like a 2 handed weapon with extra damage on top (hunter ranger, hex, action surge etc). Very high damage is same as high damage with the -5/+10 feats kicking in or a mid to high level Sorlock.
Sword and board+sentinel feat+duelist+ hex/hunters quarry can also get into the high damage territory just requires a bit more work.
I would have 5 tiers of damage.
Very low damage. Simple weapon no extra damage (wizards, Druids)
Low damage. 1d8 or so no exra damage (valor bards)
Moderate dmaage. Two handed weapon or 1d8+ a bit extra (duelist, 1d6 spell, colussus slayer)
High Damage two handed weapon+ extra or 1d8+ 2 or 3 extra damage sources
Very High Damage best in game (extra damage+ -5/+10 feats or Sorlock).
Extra damage can be a flat modifier, extra attack, sneak attack, extra dice. A Monk for example deals moderate to high damage as they get that bonus extra attack and can flurry. Level 1 Monk for example can deal 1d8+3 with a Staff or spear+ an extra 1d4+3 which puts it in the two handed+ a bit extra damage range.
An arcane cleric using a simple weapon with greenflame blade and an active spirit guardians can get up there in damage.