Thanks for the question, Oldhead.
You bring up a topic that I talk about very often these days and the way I sum things up is that in "the old day" the objective in handicapping was to determine the true Power Ratings of the teams but the in the current handicapping environment Power Ratings are the just the starting point from which the handicapping and analysis begins.
In that regard lines in the past were based much more on perception than reality with perception being at what number the action would be divided (or tilted in one direction or the other if the linesmaker/bookmaker had an opinion on the game). That was because back then there was much less information available, what information was available took time to be disseminated and the tools for analyzing the information and other data were extremely limited. Thus, if you were able to do what, at the time, was considered "advanced" handicapping you had a solid edge. I, for one, have been relying on the PC since 1980, using data base programs and spreadsheets to make sense of whatever data was available in an organized and structured way to create Power Ratings that closely reflected the "true" difference between teams. Hence, having an edge over fellow handicappers/bettors. But with the advent of the widespread use of computers and the inception of the internet and the voluminous data and information so widely and readily available the linesmaking process itself has evolved into making, in effect, Power Ratings that serve as lines, with perhaps a slight tweak depending on circumstances surrounding specific games. Perhaps the best current example of this can be found in college basketball where the widespread use of "efficiency ratings" have become more of a tool in creating lines. Thus such Power Ratings/Lines become the starting point today and the challenge is to find those games where extraneous and intangible factors are more likely to come into play such that one, or both, teams are unlikely to play to their established level as reflected in the Power Ratings and Lines. Spot play, or situational play, has become more important to me in handicapping over the years and especially in recent years.
I have maintained for a long time that handicapping is both an art and a science. The science is in the determination and development of mathematical models to evalaute teams relative to one another. The are is in the interpretation and application of those ratings to the current game being played.
Years ago I was much more scientist than artist. But as things have changed in the "information age" I have become more artist than scientist. Both disciplines remain vital in being successful but the challenge is in finding the proper balance between the two.
I hope this "philosophical" persepctive adresses your area of interest.
And, again, this reflects my opinion on the issue based upon observations and experiences over the years.