Vector line engraving low output

"Is vector line engraving weak on purpose in LightBurn?"

No. This should really only be determined by speed and power and should be no different between fill and line. In fact, once translated to g-code there’s no differentiation between a fill and line operation.

Are you dealing with a situation where you have many rapid direction changes? If so, that could cause the variable power scheme in GRBL to reduce power in an attempt to keep power consistent as the laser needs to decelerate and accelerate for direction changes.

If none of these situations seems to apply then upload a sample file where you’re seeing this.