I rather suspect the Russian Air Force could put up a decent fight. But that Russia/ Putin dont want to tangle with Israel. - because Israel has a fine defense force - and because Russia knows why Israel needs to remove serious threats like the Iranian missile Stockpiles and because Jerusalem is just not Russias target or reason for being in the area. The Saudi pipeline plan is still effectively blocked now and thats among russias Main objectives - this is mostly about who controls the energy markets
Plus, they can sell upgrades to the Syrian’s. (It’s like Microsoft or Apple - you get in cheap, but they lock you in with upgrades for life).