Try reading Parmenidean Ascent if you get a chance [1]. While not his main thesis, Michael Della Rocca argues why not treating "ancient" philosophy as philosophy proper is in error. Personally, I've studied Aristotle, and Plato, quite a bit and I couldn't disagree with you more.
> What Frege, Wittgenstein, Heidegger and other modernists did to 'philosophy' was short of completely reinventing the field from scratch.
That claim is contestable. I do agree that Frege, for one, was the first person to advance philosophical logic in 2000 years, with the previous advances made by Aristotle himself. Please study Aristotle's Organon. His singular advances in logic were astounding and not much else was done in logic until the likes of Frege appeared on the scene. What Heidegger did in philosophy was extraordinary, but it was built on the shoulders of previous philosophical giants. So what the "modernists" did was really not "from scratch".