Buks from M1-2 onwards are relatively recent updated, and TB-2 is their normal target (moreover, Syrian buks had already done a lot of it in the past). M2s are quite new, M3 is shiny new.Well, Buks are missile system from the 80s meant for fast flying fixed wing aircraft and cruise missiles. Drones are helos are their intended targets.
I.e. when Buks are destroyed - it's a fail, age of the original system isn't an excuse here.