How is it weak? Both diplomatic and economic isolation are serious problems for the Russian Federation, and covert operations is what a KGB mind immediately runs to.
“How is it weak?”
Russia was already committed in Syria at the time of the airplane bombing, and didn’t need an excuse to commit. They also don’t seek to take military action against Egypt. I don’t doubt that Putin has domestic political problems, but stopping Egyptian vacations for Russians makes them worse. I know a few Russians, and their most popular low-cost vacation destinations are (1)Turkey and (2)Egypt. Now that both of those destinations are ruled out due to the Syrian adventure, Putin has a serious domestic morale problem to deal with. I’m not a Putin fan, but I don’t think he blew up his own plane under these circumstances. Under other circumstances he is certainly evil enough to do it.