Apologies in advance, I like to think about language!

I think you have the right word for the distinction though: enslaved or coerced labor, vs hoarding of surplus productivity, vs wage theft.

I tend to think of language in terms of interpretative vs prescriptive usage. In legal, engineering, and other regulated domains there is a very prescriptive use of language where specific words have specific meaning and synonyms or equivocating just aren't acceptable.

Outside of those, interpretive use of language reigns where people can be creative, and we use and reuse words all sorts of ways without much issue. Sometimes words with very specific meanings in prescriptive domains are also widely used to mean something different in interpretative domains, and we just clue in on context.

That said, personally I'd find it confusing to try and educate people on an interpretative meaning of wage theft that was thematically similar while being distinctly different from the legal definition of withholding pay or benefits earned. In that case, context wouldn't clarify and you would have to explicitly define your meaning every time you use it.