Cicero was a conservative in some ways. But I don't think he was particularly prejudiced or classist, for the time. Remember that he was technically a plebeian himself, although obviously a privileged and successful one.
Cicero's father was of the equestrian order, not patrician but definitely not plebeian. Think upper middle class from the midwest who goes to the right schools and ends up in DC.
Pompey, Crassus, Cicero, Gaius Marius, Mark Anthony even Octavian (before being adopted by Ceasar) were technically all Plebeian. By mid/late Republic the Plebeian/Patrician distinction had lost almost all meaning, as most Patrician families had died out or were surpassed in wealth and political influence by more successful Plebeian families.
The Equites were purely a social/wealth based class, any Roman citizen could become one if he we satisfied the wealth requirements.
Calling equestrians the upper middle class is not accurate. They were firmly upper class, just the lower portion of the upper class. If the senatorial class was roughly the billionaires, then the equites were the ten and hundred millionaires. Perhaps not as rich as the very top of the upper class, but still a league above the upper middle class.
Yes, calling Equestrians the upper middle class is not accurate. Our classes don't accurately map on to Roman classes; it was just a flip remark. Nouveau riche doesn't work either.
However, the Senatorial class was not an economic distinction either but rather an aristocracy. Even in the Late Republic these were old families who had had Senators and Consuls in their heredity. There were fewer of these clans, 14 at the time of Caesar (of the Julii clan). Cicero by comparison was of Equestrian rank and a New Man, novus homo, in the Roman political world.
Equestrians weren't knights anymore, expected to field a horse, .... The Roman legions had been professionalized by then. There were property and suitability requirements enforced by the Censors.
Technically it was illegal for senators to engage in any commercial activity besides agriculture so they still had to really on the equites who directly exploited the natives in the provinces to give them their cut (tax collection was privatised in the republican period). So it's not unlikely that there were individual equites who were more wealthy than many Senators.
That's fair, since senatores was a political class, not an economic class, and equites was technically the top economic class. I tried to simplify things to make the analogy possible, and I think the spirit of it is instructive even if the details could be more complicated.
The important point is that no one should mistake the equestrians for anything close to even the top end of the middle class.