Ownership means having power, having control, over the thing you own.
An authoritarian government that maintains control over the means of production, no matter how much they nominally "belong" to the workers, inherently alienates the workers from having power and therefore from ownership. In that sense it is state capitalist.
You cannot have it both ways unless you change the meaning of words like "own", or "authority". Your own description of leftism precludes authoritarian methods.