Rob, I agree with most of what you are saying.
I think, and correct me if I am wrong, that the "can't take % to the bank" was referring to being so concerned with tweaking everything to the point where we forget what matters: sell the job, bill the labor, make some profit.
We all know how our shops we be run in a perfect world where work mixes were always predictable and we had the "right tech for the right job" each and every time. But, hey, that ain't the way it happens. If there's an opportunity to sell a brake job and all our lower paid techs are busy but a higher-paid guy has available time, then he's gonna do the job and we're gonna get it out the door. Sure, the profit percentage shrinks a bit, but a little bit of something is better than a whole lot of nothin'

I gotta tell ya, when we stopped fussing so much over percentages and hours-per-repair order...and started thinking "any sale is a good sale"....our *dollars of profit* went up dramtically. Right now our effective labor rate and gross % on labor are as low as they have ever been in years.....and departmental net profit in *dollars* has never been better.
We have seventeen techs (excluding detailers and accessory installers). Two are lube guys, and three are heavy line. Beyond that, the other twelve do whatever job they are capable of doing, regardless of pay rate or the type of work. With 5 carlines and the crazy work (and brand) mix that we have coming thru the door, there's just no way to "fine tune" things. But, hey, that's us. As we all know, what works in one store make not work elsewhere...for about a hundred different reasons.
Cheers everybody
Doug