"Is economic (wage) slavery actually slavery?"
This boils down to one issue: are the wage workers prevented by the force of statism from becoming the employers instead?
If the employees are freely allowed to become employers, the system is self-balancing and each person will fill the slot that suits them. There's no wage slavery if a wage worker is not stopped by force by becoming an employer instead.
Even if an individual employee is not in a position to become an employer, provided plenty of others can make the switch then it protects the other employees too, by keeping wages as high as sustainably possible.
On the other hand, if the state uses force to impose quotas, licensing, forced monopolies, registration, or even just bureaucratic overhead so high that a one-person business can't realistically cope, then it cleaves society into employees and employers and virtually guarantees the existence of wage slaves.
