No one single armored vehicle will ever be the answer for all combat situations and even unpredictable scenario ones. A well balanced army will always consisted of both a MBT and IFV one way or another. During the Vietnam war era people used to think Air Cavalry (helicopter carrying troops like the UH-1 Huey) will replaced the armor cavalry completely, but it never did. Different scenario, terrain, weather, and political aspects will always play a vital role in what to weapons to use.
That is true, as there is no single vehicle that will take on all combat situations, since each vehicle have many variations.
I am always wondering why Russia toy around with BMPT style turret and not a BMP-3 style turret for MBT chasis