i'm sure i'm not the only 1 to do 5000 rb's and never get a wt. this doesn't feel very random. if drop rate is 2% that doesn't mean i'll get 2 wt's every 100 rb's. its still 2% per adv, my maths aint gr8 but I think that means the drop rate actually diminishes over 100 rb's to .02%, if adv's taken as a whole. In real terms, u do 100 rb's and still only have a 2% chance to get 1 wt.
Would a system that raises the chance of getting a wt everytime u fail work better? say every 10 rb's, with no wt in loot, the chance rises by another 2%. up to a maximum of 20%. then reset when u win a wt. This could be applied to all slots so as to mix the loot up a bit more if necessary.
along with all the other info kept about players on servers I don't think tracking loot % would mean much more load.