Wrong!!! The solar controller has no clue about what is getting to the battery. Its output goes to loads first and anything left over goes to the battery. It does not know how much is going to what. Same thing with a converter.
You need a battery monitor to know what is happening with the battery.
EG, if the solar controller says it is putting out 5 amps and the battery monitor says it is getting 2 amps, that means there are 3 amps going to loads.
If your battery monitor says the battery is getting 75 amps from the 75 amp converter and the furnace comes on, you see a drop to 67 amps on the monitor which means the furnace is taking 8 amps of the converter's output and the battery is getting the 67 amps left over out of the 75.