I think it's worth keeping 'wage theft' to that particular definition, to help with tackling what is a big problem and legally recognised (as illegal). And, as someone else said, so workers don't dismiss it as a far-off ideal and miss the chance to fight for their illegally-stolen wages.

Wage theft in the sense of theft of fair share of generated value/profit, needs a new name.

How about profit theft? Value theft?

After all, calling it wages already accepts the idea of owners and employees.