It seems to me that there are different stages of leading. Thoughts? I would identify 4:
1. "no" leading. This is a misnomer, as I feel that even the best lube will not work absolutely perfectly, and if you hold your muzzle to a strong light and look at the lands, you see a slight silvery color. If this wipes out in 1 or 2 patches and isn't plated to the bore, then I say all is working fine. Lube is good, bullet fit is good, velocity is good, etc.
2. "wipe out-able" leading. This looks like number one above, but starts to effect accuracy. It still cleans out with a minimum of effort.
3. Streak leading- when the leading starts to jump the lands/grooves, is visible in splotchy patches, etc., something bad is happening. Either you are pushing things too hard for your lube, the metal is too soft, etc. Probably due to too much friction or heat?
4. Filling the grooves- this is when you actually start to see shards when cleaning, and cleaning takes forever. The bullet is starting to shed itself. I often have this with pitted milsurp bores, but that's another issue.