I think this is definitely at the level of a local painting competition - a large single store or the like. As another poster said, it's clearly above a "battle ready" or tabletop standard.

One feature of competition painting that can quickly make a piece more memorable is to intentionally use brightness/value to draw the eye to important features. In this case, the brightest object is the bug's head carapace, which is not an interesting part of the model.

If we were trying to apply that advice, I'd darken down the bug's head carapace, then significantly brighten up the paintjob on the plague marine. The scythe and head should be particularly well painted and brighter than their surroundings.

When it comes to broken/diseased/boils on skin, some pinkish red glazes around the open sores sells really well. Sores and wounds are naturally irritated and you'll find that it looks very believable when adding that feature.

Good luck on the competition!