First, I never stated that Ovation guitars were POS. Ovations, IMO, are niche guitars used for a very specific purpose where within that purpose it works well, although there are still many better choices IMO. Like I said earlier, it's used often onstage due to it's plug and play nature that yields a pretty good amplified sound without much hassle.
Of the 7 artists that you listed, only 3 of them are considered guitar players, first and foremost (Chet Atkins, Mark Knopfler, Jimmy Page). Although they've all played an Ovation at one point in time, none of them choose Ovation as their main acoustic guitar of choice. Chet Atkins plays his signature Gibson acoustic/electric, Mark Knopfer prefers a Martin 000-40S, Jimmy Page prefers a Martin D28.
Anyways, there are Ovation fans out there and if it works for them, the more power to them. For me, there are better choices that I prefer as a player such as guitars from Nick Benjamin, Huss & Dalton, Santa Fe, Martin (with the exception of their entry level models), Larrivée and some of the higher end Taylor. Why? Quality of workmanship from fretwork, bracing, neck setting, binding, etc... to the acoustic tone and projection of sound which are all far superior to the ovation. For stage, a piezo system can easily be installed and some guitars such as the Martin OM-28E come with the outstanding Fishman Aura system that works even better for stage work than the Ovation.
Finally, all of the guitars from the brands I've listed typically are more costly than Ovation, but for me, someone who has been playing for nearly 40 years, the extra cost is well worth it and quite noticeable. For someone who has just started playing, it may not make sense spending $8000-9000 for a custom made Nick Benjamin and the differences may not be appreciable. With that said, from what I've learned over the years, whether it be guitars or hifi gear, there is no one size that fits all.
In it's bare essence, it IS valid.
You just stated that it works well under a given set of circumstances.
Those circumstances being as a non-mic'd stage guitar.
A true POS guitar will not perform well under any circumstances (unless maybe you are using it to bash someone over the head

Again, if it's a POS, it's a POS that many famous people have used very effectively to earn a better living than the vast majority of our country.
I was just describing the concept of people painting with very broad strokes without the ability to "back it up".
Not that their fame means they know anything about guitars, but some of the folks who use or have used Ovation:
Cat Stevens
Chet Atkins
Robert Plant
John Lennon
Glen Campbell
Mark Knopfler
Jimmy Page