Botched cornices by a family member

Had a family member (30 years exp. With a carpentry business mind you) do a kitchen renovation for us. All is mostly okay except for the worst cornicing job I’ve ever seen. I’ve been spending all day sanding and priming to try to conceal it but it’s not helping.

When he first put the cornices on, one of them fell off. Instead of putting a new one up he just slapped the broken one back together which has left us with a lumpy cornice (pic 2). There’s been too much of whatever wet/plastery material used to adhere it.

The fact it’s been done sloppily over the cabinetry also means that it has affected it.

Any tips to try to fix this myself or does it just need to be redone?

Don’t need a hard lesson about paying family to do jobs please spare me more misery, ta!