So, thanks for the input !
From here and some forums, it looks like the main issue is a feeling that two practitioners of the same level should differentiate by characteristics. This is obviously one of those things that has been struggle over since the first skill based RPG showed up (RQ ? Traveller ?); and while it does make intuitive sense, the simple solutions (mods based on characteristics) rapidly become too much -and this is especially true in a 2d6 system. Would a reframing of the issue help ?
My "ah-ha" moment was this: why do two characters with the same skill level need to be differentiated in their results ? The short version is this: consider the two doctors at medic-3, one with DEX 14 and one with Dex 5. One can assume that they should have different outcomes based on their Dex, but why ? I'd suggest that the most important differentiation would be in how long and with what effort it took them to get to level -3. The naturally gifted surgeon probably took less time to get his level 3 than Dr Allthumbs -but they both got there. Now, if Allthumbs had only taken the time and effort that Dr Giftedpratt took, he would only be at level 2.
The more I look at this, the more it seems at least as reasonable as assuming two equally trained Doctors would differ significantly in their results -especially as their effectiveness would be part of their rating.
Logic check ?