It is possible that you have worn clutch plates or even clutch springs, but I have replaced old plates with new ones and when I compared the old with the new there was no wear, If the bike has been standing for any length of time the plates could have dried out and become coated in a very shiny gloss that prevents grip..
Obviously you should not use oil with friction inhibiters on a wet clutch system that relies on friction to work. And as already said you can't expect a hydraulic clutch system to work at maximum efficiency if the fluid is dirty and worn out.
Easiest first, check that your oil is formulated for motorcycles with a wet clutch.
replace the hydraulic fluid into a cleaned system. ride for at least 500 miles to allow the oil to circulate, and then if all else fails change the plates and springs.
Just advice, feel free to do something else instead..
John.