My observations/opinions are:  the pitting is due to Suzuki's sub standard metallurgy they have used on their off road transmissions for the last 40+ years.  This is one of the reasons the LTR450s also have a lot of transmission problems.   They use good metallurgy in their street bikes, why not in their off road products??

Higher viscosity transmission oils will tend to slightly reduce the pitting but at the expense of the likely-hood of clutch slippage and a slight power loss.