IMO, unless it's above 250k, run. Not only will that be a total hellhole to work at, but everything he does there won't matter at all for his next job. It'll essentially be a black hole of experience that just saps his energy but gives him absolutely nothing back.

It will only hurt his career, and we have such a high ceiling on our potential income that wasting time on a job that pays well in the moment but gives you nothing for the next one is just foolish. Every single job you take should be setting you up for the next one in some way. Avoid any company that has you working proprietary stuff. If the skill isn't transferable, it's not worth your time.

OP, run far away. Another couple months of searching for a job looks a lot better on your resume than a couple years at this place.