In no way could you apply your "concrete objective measures" from one artist to another, or from one movement to another. And since you clearly can't do that, your "concrete objective measures are neither concrete, or objective. In fact, many artists and artistic movements made a direct point of rejecting the standards and aesthetics of the movements that preceded them; so how could your "measures" possibly be of any use in defining art? Please apply your "measures of artistic excellence" to Marcel Duchamp's "Fountain" and explain why a commercially-produced urinal is regarded by many critics as a "landmark" in 20th century art - critics whose opinion you would have us defer to regarding what is, or is not, Art.
"Some opinions are more valued and therefore more valid than others. For instance, people who know the field and therefore know what they’re talking about, rather than an accountant or a real estate agent."
Opinions "more valued" by whom? And we're not talking about accounting principals, or real estate law, subjects that require detailed and specific knowledge (and actually do have objective measures), we're talking about what is, or is not "Art" - a subject, which, by it's very nature has an appeal to people from all backgrounds and fields of expertise. If you have to defer to a group of self-selected "experts" to explain it, it isn't art.
"Rockwell’s biggest problem was that he was a commercial artist producing vast amounts of thematically similar work, work that veered too far into cartoonish for the more conservative art critics who deemed his work to not be serious art."
Rockwell was a commercial artist who worked for clients - if some of his work was thematically similar, it was because that was what the clients wanted. It was no different from any Renaissance artist you care to name working for the clergy or the nobility - a whole lot of "thematically similar" work was produced by those hacks /s. As for "producing vast amounts of thematically similar work" there was this critically-acclaimed guy, you may have heard of, named Andy Warhol. Feel free to expound on his artistic genius. You've also described some of Rockwell's work as "cartoonish" - Rockwell used humor in much of his work, a perfectly valid emotion to appeal to, just as valid as any other emotion an artist might try to use.
"Sounds to me as if you just “like” Norman Rockwell for sentimental reasons and because it’s pretty. Furthermore, you’ve become fixated upon some stereotypical image of an art critic based upon the admittedly very political northeastern art establishment that foisted off a fair amount of deliberately offensive junk as art..."
Like Winslow Homer before him, Rockwell's roots were in commercial art, but to suggest that that disqualified him from being great is ludicrous. Rockwell is not a particular favorite of mine, but I absolutely respect his artistic abilities, and I find the opinions of those, like you, who denigrate the man and his artistic efforts, quite tiresome. It's even more offensive when you repeatedly rely on the opinions of "art critics" as a justification for why Rockwell isn't really an artist when those very same critics acclaim other "artists" producing dog crap (sometimes literally).
The stereotypical northeastern art critics are precisely the ones who are defining what supposedly constitutes "art" today, which is precisely why I reject their opinions. I've seen what they like and promote. And for the record: I have a degree in Studio Art, work as a graphic artist and I've taken more art history classes than I care to remember.
My goodness, what a screed. Go shake your fist and yell at clouds over the unfairness of it all.
If I were to follow your lead, there would of necessity be no objective measure of beauty or truth. And yet it’s you who believe yourself to be capable of rendering such an assessment.
It appears that you’re carrying over some internal, mental debate with someone else who’s gotten under your skin, perhaps someone who deems your commercial art unworthy of a gallery. I suggest you take it up with them.
Regarding Warhol, I suggest you peruse the thread and get back to me.
Now, take d e e p breaths, back away slowly and go to your happy place. It’ll get better, I promise.