No one at Nato is or was talking about winning a Russian-Nato war at the Fulda Gap or at the Suwalki Gap -- or at any gap or one place, locale, area.
V Corps' 11th Armored Cav Division was meant to delay, not hold the Fulda Gap against Soviet Russian-Warpac forces. V Corps was deployed along the easy plains at the West German side of the Gap. 8th Infantry Division was integrated with 11 ACD. In contrast and if Nato had wanted to make a stand using the Gap as a defensive barrier, the Nato order of battle would have led with the 3rd Armored Division, which it did not. 3 AD was not positioned up front at the Gap because Nato considered Fulda impossible to hold as a defensive position. Neither side could hold Fulda as a defensive position. You have overstated Fulda as a viable natural defensive barrier. You have also put Russian-Warpac forces exiting the gap into mountains that defend themselves as you put it, which is not the case. The gap is in the mountains and runs through 'em then opens to easy plains on grassy lands with streams.
In a conventional war, the 11th ACD was expected to delay Ivan by 24-48 hours, then fall back through 3rd AD lines and get ready for the next Soviet Russian-Warpac offensive strike. Coming at Nato were to be the Soviet 8th Guards Army with four Motor-Rifle and one Tank Divisions, with the 1st Guards Tank Army having four Tank Divisions following behind. Warpac at Fulda included the East German 3rd Army, with four Motorized Rifle Divisions and one Tank Division. Days 1,2,3 would belong to the attackers, while days 8, 9, 10 would belong to Nato -- it would have been the dayze in between, 4-7, that would characterize the nature of the war to include conventional, chemical, biological, tactical nuclear.
Yes we note here definite zero-sum faucets of the Fulda Gap such as Patton charging through it into the heart of Germany. And that Napoleon marched his grand armee through Fulda when he advanced, then dragged it back through again when he retreated. Yet the Nato approach was to make Fulda a battle zone in which engagements would be ongoing during what everyone expected would be a Russian-Nato conflict of a brief and decisive duration. Likely fewer than ten dayze. So we see that the Fulda Gap as well as other gaps through history have not only been a zero-sum impregnable feature of defense.
This is also the case with the Sawalki Gap between Belarus and Kalningrad to Nato in its strategic planning and positioning. So the takeaway for you in this is that a gap is not necessarily or always a zero-sum gift to the side on defense, that a gap most often has several routes through it as Fulda does have and which open to easy plains rather than to more mountainsides; and, that a gap commonly connects economically and politically common peoples separated by nature or warlords if not both. That neither the Fulda Gap nor the Swalki Gap are decisive to a war in Europe.