"You can tell how good a compressor is by counting the number of stages that have variable pitch stator vanes. They're a mechanical complexity that you'd only ever use to maintain adequate operating margins (and prevent disaster!) in pursuit of efficiencies not achievable by other means."
I hear what you're saying, but first you gotta' define "good".
Let's compare two widely used engines with which I'm familiar, having flown several different aircraft using these engines in various forms. The P&W J-57 which was used with an afterburner in the F-8 Crusader and F-100 Super Saber and without AB in aircraft like the B-52, Boeing 707, and many others. And the GE J-79 used most famously in the F-4 Phantom, the F-104 Starfighter and even in Graig Breedlove's Spirit of America.
The J-79 was a single spool engine featuring a compressor loaded with variable pitch stators. It was light weight and efficient with absolutely fantastic throttle response. The 17 stage compressor produced a 13.5 to one compression ratio. You could argue that the variable stators made the engine resistant to stall, but it's equally as correct to say that they were necessary to avoid engine stall because of the high compression ratio. Of course, there are trade offs. The J-79 smoked badly and if you so much as spit down the the intake, the thing would come apart often taking out the adjacent engine as well.
(standing by for hostile fire from ex-F-4 types in spite of the fact I'm one too)
The J-57, on the other hand, was a twin spool engine with fixed stators producing only an 11.5 to one compression ratio. Its thrust to weight ratio wasn't quite as good as the J-79 either, but it was naturally resistant to compressor stall. Plus you could toss a Yugo down the intake and it might belch and fart a little bit, but it would grind up most anything and wouldn't quit; a feature greatly appreciated by we who prefer single engine aircraft.
So yes it's true, as you say, counting variable stators is one way to measure a compressor's "goodness" especially if you're talking about efficiency or thrust to weight ratio. But when you factor in purchase cost, maintainance cost, complexity, and reliability (especially in combat) I would argue that the measure of overall engine "goodness" involves more than counting variable stators.