Indisputable fact in your mind, perhaps, but others might choose to dispute it.
Keep in mind that classical music runs a very wide gamut, from Beethoven and Bach, to Mozart, to Mahler, to Debussy and a whole pantheon of other composers. I wouldn’t put Mahler, for example, in the same genre of classical as I would Bach, although they both wrote classical music that is performed by orchestras.
And can you really put Saint Saens in the same box with Mozart or, for that matter, Grieg?
And where do you put Stravinsky, Ravel, and Prokoviev, who were 20th century composers who weren’t strictly speaking like any of the older guys?
My feeling is that your assertion is essentially too broad and too all-encompassing. Some 17th and 18th classical stuff was crap, and some 20th century stuff is truly excellent.
Perhaps you can focus your question a bit more?