It's a hard truth that capital garners the majority of the additional profits from labor efficiency increases.

I struggle with this. Yes, it seems almost a law of nature that fitness begets more fitness. But surely we can structure society to be above mere nature?

So what's the mechanism to protect against it?

Market forces don't seem to work too well.

Corporate taxes would/should work, if our government weren't also co-opted by capital?

Unions?

UBI?