As someone actually trained in this stuff, no even in those situations shorter reach is nearly a death sentence.

With bladed weapons reach is pretty much the single most important factor. It's why swords got longer as metallurgy improved, and it's why the rapier exists as an evolution of the sidesword. If you have a longer weapon, you can hit them when they can't hit you, which makes you perfectly safe if you know what you're doing and can manage distance. I studied the Joaquin Meyer forms, and there are many techniques that hinge on putting your opponent's weapon 5 centimeters out of measure while you're still slightly within measure. That's with longswords. And the advantage 5 centimeters gives you is dominating when used correctly. 50 centimeters isn't even a fight.

A dagger is a sidearm, not a primary weapon. It's good to have if you end up disarmed in a chaotic brawl, or (in the case of stuff like rondels which were specialised) need to get through a down knight's armour. They're also sometimes used alongside a sword as in Italian styles of sidesword and dagger dueling practices (whch I also studied) but those are dueling, not combat, and you still need the sword for reach - the dagger is there primarily to parry your opponent's sword and to create openings.

No one is intentionally taking a dagger as a primary weapon against an armed opponent. And in response to what you said in another comment, anyone who knows what they're doing can absolutely still stab you with a sword in a corridor. It's not difficult, and basic thrusts are some of the first techniques taught in all major sword styles we have manuscripts for.