It's nebulous and really you're only placing yourself on a bell-curve.
I'm adding my complaint about this now because in other threads we talk about a good game needing targets to aim for ... raid gear, ability to meet certain thresholds, etc.
AC/to-hit used to be like that, but admittedly too small a scope (single d20). Instead of widening the range for orange/red/purple +/or epic mobs, now we have something where everyone basically can hit and be hit. Instead of having a goal to shoot for, now we're playing a game of "how long will this take".
And we all get a trophy. Because competitions where everyone gets a trophy are awesome.
- the up past his bed time grumpy guy