Also when the economy becomes more centralized and bigger companies swallow up smaller ones, you should expect more cartels. That is just logical.
I didn't say I had evidence but I know the number of competitors for positions in the UK has been going down, not up. The price for labour however has not shifted.
This is indicative of fixed prices, in this case wages.
Does you think the prices for turnips can be fixed but not that of plumbers? It's all the same thing.