I don't think it even makes sense to calculate US wages as a percentage of US GDP, because if I'm understanding the definition of GDP correctly it includes econ

I don't think it even makes sense to calculate US wages as a percentage of US GDP, because if I'm understanding the definition of GDP correctly it includes economic activity done in non-US countries with non-US workers. In particular, it's defined as the total value of finished goods produced in the country, which I think means that it includes the cost of imported components and raw materials even though that money doesn't end up in the US at all. So if production of those raw materials and components moves from the US to other countries - which it probably has done, quite a lot - it wouldn't affect GDP but would affect the actual pool of money that US workers could get paid from. Actual labour share of the actual money being made seems to be pretty hard to measure accurately, from what I can tell.