So, they didn't detect anything until the drones were almost there and scrambled to respond with the only thing around - a shiny new Su-57 being kept safely away from combat?
TBH these kinds of small, relatively slow moving and low flying targets are a terrible match for jet fighters so it's not a surprise they didn't stop most of the drones. I think we'd see other modern fighters struggle against them, too, especially without radar support from the AA batteries they're using to protect Moscow, Kerch, and Valdai.
European Russia is in range (and the majority of the population and industry), but assuming the Omsk attack is about the current outer edge of Ukraine's strike range, most of Russia is still out of range. The country is like 9000km east to west, just unreasonably huge.