From what I have seen, the Herald, marksman and protector are seen as the weakest in the game, so my question is how would you improve them

For me a few things

Here is a simple solution that also fits the theme of the herald

Old Battle Cry: 1 VP, applies Fury to all allies in 4m area, upgrade increases area to 6m.

New Battle Cry: 1 VP, applies Fury to all allies in 5m area, foes who are engaged or at less than 50% health in the area gain scared (This unit causes an extra 10% morale loss when they die. )

upgrade increases area to 10m and applies scared to all foes in the area.

Marksman Old Aimed Shot: 2VP, 8m range, Deals (70% DEX) damage to the target. Damage increased by 5% for each metre separating the target from this unit. Upgrade makes it so critical chance also increases by 5% per metre.

New Aimed Shot: 2VP, 8m range, Deals (75% DEX) damage to the target. Damage increased by 5% for each metre separating the target from this unit. If target is engaged, increases critical hit chance by 2% per metre of distance.

Upgrade: 10m and makes it so critical hit chance and critical hit damage also increases by 2% per metre of distance regardless of the target being engaged or not.

Protector Old Encouragement: 1 VP, applies Protection (-30% damage received) for 2 rounds on all allies in 6m area. Upgrade increases effect length to 3 rounds and area to 10m.

New Encouragement: 1 VP, applies Protection (-30% damage received) for 2 rounds on all allies in 6m area. Also removes vulnerability on engaged allies

Upgrade: increases effect length to 3 rounds and area to 10m. Removes vulnerability on all allies in the area