"Why Does The Death Star Have Such A Stupid Weakness Of An Exhaust Port?"
"Cooling things in space is difficult as heat needs somewhere to go. An exhaust vent is a perfectly reasonable thing to have station is the size of a small moon that's obviously going to generate a lot of heat and other such things that needs to be vented. The movie also outright tells us that this is not the only exhaust vent the station has. In the briefing scene it mentions there are multiple exhaust vents, it wasn't a single vent.
The Rebel pilot also complain about the 2m wide port being too small to hit. Their first torpedoes are unsuccessful even with the targetting computers, it's only Luke using the force to time when to fire that works, so it is not some huge glaring uneccesary weakness. It's an integral part of a giant space station that even skilled pilots with computer-targeting couldn't hit, it wasn't some significant weakness in the first place.
As part of that, there's the "Rogue One explains the weakness!" thing. No, it doesn't explain the exhaust port - the weakness added by Galen Erso is that the reactor when hit will cause a chain reaction. That specific exhaust port is just identified as the most appropriate one to use."