I suspect you might have the lowest powerline adapters...do you have something like av500/600 or did you get the newer ones that have 1000/2000 numbers. Many people will get about 130mbps on the top end units.....which of course is still far below gigabit speeds.
Generally this is the standard network lie you see. The 80mbps is likely the total network bandwidth shared between all devices. In your case you likely only have 2 the router and your pc but there can be many more. This is pretty much your half duplex problem. Almost all traffic has send and receive but they can't actually happen at the same time when you are running half duplex. This kinda means the maximum rate you would get would be say 40mbps but it is more complex because of how the switching between devices is done so it can be more or less.
A real ethernet cable has 1gbit transmit and 1gbit receive. If you would use the same bandwidth number you could call this 2gbit except ethernet can really do 1gbit in each direction at the same time.