You will have to ask the Russians about that. What makes you think the Russians can not build an effective air defense system? This is their most advanced deployed system. Probably similar in ability to our Patriot air defense system.
Will Russians or Syrians be operating the systems?
They don’t have a wondrous record of success. In Iraq, their vaunted T-72 tanks were a miserable failure as were their advanced jet fighters. They had some success with SAM’s in the 73 war but Israel really didn’t have experience with SAM’s. Over time, the Israelis were able to defeat the SAM’s.
Russian SAMs have failed over and over again throughout the last 40 years. Their missiles are usually better than the radars attached to them. They are much better at promotion than design.
The new system is a decent improvement on a 30 year-old technology. Isreal can defeat it, but will have some losses before completely eliminating it.
The numerous Arab dance parties centering around the wreckage of shot-down Israeli and American fighter jets is proof positive of the effectiveness of Russian air defense systems.
Oh, wait...