If you wanted to block up those vents you need access to them. If you've buried them beneath tonnes of rubble you're never going to access them and they're going to function just fine 90% of the time.
Good luck finding them though. I'm also inclined to believe that it isn't an interconnected system of tunnels but instead several different groups of tunnels.
Not just pointless. Actively bad.
If you wanted to block up those vents you need access to them. If you've buried them beneath tonnes of rubble you're never going to access them and they're going to function just fine 90% of the time.
Good luck finding them though. I'm also inclined to believe that it isn't an interconnected system of tunnels but instead several different groups of tunnels.