I found that there's one school at one of the many universities where I teach which last year added 14 "staff" positions for every TT position. Does that ratio seem a little skewed to you? What's a normal ratio?
In his book
Tuition Rising, Ronald Ehrenberg shows that research universities typically have a ratio of 4 or 5 FTE staff to 1 FTE faculty; at baccalaureate colleges it's more like 2 to 1.
Ehrenberg doesn't differentiate between TT and non-TT. But there are innumerable signs that the number of TT positions, both new and overall, have been declining steadily for several years.
It's my belief that the decline in TT jobs is largely a function of two forces: the end of mandatory retirement at 65, which makes it difficult to adjust to variances in enrollment and impossible to plan replacements; and the current flood of Ph.D. graduates. That makes it possible for institutions to depend on contingent labor; there is plenty of labor, so the classes are covered, and the tenured are content with their own teaching assignments and other working conditions.
Ironically, the high quality of most adjunct teaching makes this solution more palatable. If there were indeed a clear distinction between them -- if all adjuncts were terrible and all TT faculty were excellent -- then institutions would see enrollment decline such that they would need to add TT positions, not remove them.
Maybe you, lotsoquestions, are on to something with your search for the "normal" ratio. I suspect that if US News decided to include percentage of adjuncts as a criterion in its odious "rankings," you would indeed see many institutions adding TT slots. (It wouldn't fix everything, of course, but it would be a start.)