According to this answer increasing blade solidity increases the blade area by either enlarging chord or increasing blade count both of which reduce efficiency via reducing the lift coefficient and increasing friction.
However, in fan maps of turbofans the efficiency of the fan is as high as 90%.
The word efficiency seems overloaded, meaning different things in the case of lightly loaded propellers compared to highly loaded fans.
What exactly are we measuring the efficiency of then? If it's just measuring the efficiency of compression, how can we relate the "efficiency" of highly loaded fans to that of lightly loaded propellers?