Probably you are right, they are essentially wrong. I admit being ignorant enough about music that I don't know how such and such composers music should be played, if going by the score & time period, and do you know what, I feel all the better for it.
My non-musician take is, if I'm not playing the music, then I'd rather be ignorant and listen to these incorrect interpretations without feeling the music has been desecrated (as some seem to feel). In a number of ways, I feel they musically hit the spot more so than modern orchestras that play like metronomes, always on the beat, always the same (often abbreviated) note length, nothing goes ahead, nothing drags behind, all of a similar colour throughout.
I do wonder if we were to ask Beethoven himself whether he wanted such interpretations, that he had a singular idea of perfection for a certain piece, that not only could be attained, but should be attempted in more or less than same way by all conductors and orchestras, whether he would say yes. I don't know, but my feeling is that the playing of today is not really any less peculiar/particular to a time than that of the 1930s and if we had Beethoven to refer to, he'd likely find them equally foreign to how music was played within his lifetime.
But isn't that some of the point of music, a little sense of the nervous, of the immediate, of a creation happening right now, rather than something honed to a sharp point over endless rehearsals. Another issue I have with modern orchestration is that it all sounds like they have played it 1000 times before, there is no element of risk, no chance of a violinist or flutist holding a note too long or coming in at the wrong time and this seems to give the music a static feeling. To my mind there is such a thing as being too perfect and it can kill music. Without any sense of risk, is it really music?
Listen to this Brahms violin concerto with Toscanini and Heifetz. They seem to be fighting throughout over tempo. Toscanini wants to go slower and Heifetz, as per usual, wants to race ahead. The two titans are butting heads, but this sense of tension, at least to me, is magic. Yes, it is scattershot, yes, it is haphazard, yes, all kinds of liberties might be being taken, but it is living, breathing music, not something suspended in aspic.