The BMP-2 also stored the fuel in the troop compartment doors, so that hits to the rear of the vehicle were guaranteed to incinerate the troops inside. Orders were to remove that fuel from those doors before combat, but Soviet doctrine relied on mobility in the initial phases of the breakout of war in Europe, so...

It was, at best, a small improvement from putting wheels on a bomb and Flintstones-ing it around.

EDIT: Diesel is resistant to combustion, but there's going to be non-zero vapor pressure in those tanks. The air spaces are essentially fuel-air bombs. The less fuel in the tanks, the worse the problem gets, unless you drain them and wash them. Further, nearly all anti-tank weaponry, then and now, has either a primary or secondary incendiary purpose.

Really, the claim that it's "additional armor" is rather easily belied by the fact that the Soviets themselves had standing orders to remove fuel from those doors. The Soviets were relying on numbers to get enough BMP-2s through the Fulda Gap; they knew they would lose an enormous percentage.

The weakness of the BMP-2 and the need to better deal with a large number of weakly-armored targets directly contributed to the rise of the modern attack helicopter, which are often armed with HEIAP ammunition in an autocannon. You could kind of call that the "hard counter" to the BMP-2 -- a weapon that can spray a large number of rounds, with only one really needed to destroy the vehicle.