Steel Idler Problem

Bought some steel idlers from eBay. But im' un-sure which brand they are. The hole in the middle has been drilled straight through and a circlip has been used to seperate the bearings if that helps any.

The idler wore down my lightened second gear and it was making my gearbox insanely gritty and covered the inside with metal shavings. I mean covered! My second gear (botom shaft one) now has a kinda cool metal coating. Ultramaxxed on the cheap!

Anyway, what I wanna know is how can some use steel idlers if they wear down the primary gears? Unless the lightened gears or my steel idlers are made of the wrong material?