The worst thing you can do to a hard worker is give them everybody else’s slack as a reward.

Reliability quietly turns into a tax. The person who always finishes gets handed whatever nobody else did, because that is the safest place to put it, and the reward for being dependable becomes more work. From outside it looks like trust. From inside it feels like being punished for being good, and it is how willing people burn out or quietly stop trying so hard.

Look at who absorbs the leftovers in your group and work out how much they are carrying. Move one of those jobs to somebody else, even if it gets done worse. Give the reliable person something they actually want instead.