https://www.quora.com/Why-are-most-Russian-fighter-jets-bigger-and-heavier-than-American-jets
Russia has indeed opted to focus on bigger and heavier aircraft than the US. While the US has opted to concentrate on smaller designs like the F-16, F/A-18 and F-35, the Flanker family is currently the backbone of the Russian Air Force. Flankers are roughly equivalent in size to the US’s F-15 and F-22, which were only procured in comparatively small numbers.
Russian defense planners believe that airbases are becoming increasingly vulnerable to stand-off munitions like cruise missiles. Fighter aircraft are indisputably one of the most powerful classes of systems on the modern battlefield. As such, in a conventional war an emphasis would be placed on knocking out the other side’s fighters in the first hours of combat. Fighters can be particularly vulnerable, because they spend most of their time at fixed bases. The location of these bases is generally known to the other side. These bases are easy targets for modern precision-guided weapons like cruise missiles.
To mitigate some of this vulnerability, the Russian Air Force has focused on acquiring fighters with longer ranges. This allows Russia’s fighters to base outside the range of many stand-off munitions. Additionally, it increases the probability that any munitions fired against a base will be intercepted before they manage to reach their target. It also increases reaction time. If the fighter pilots know an hour in advance that a strike is coming, they might be able to get their planes in the air, avoiding the destruction of their aircraft.