I rather suspect the Russian Air Force could put up a decent fight. But that Russia/ Putin don’t 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 Russia’s target or reason for being in the area. The Saudi pipeline plan is still effectively blocked now and that’s among russia’s 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).