The exit would've been for if they surfaced (that plus a life raft presumably)

When you have a fire and need to surface, it's going to do a lot of good. One of the Apollo crews burned alive because the ground crew couldn't unscrew the hatch fast enough during a pre-flight checkout. One of those astronauts, Gus Grisham, nearly died a previous time when the explosive bolts on another capsule fired early which caused the capsule to take on water.

The problems here are just several fold: maybe the door won't help you at depth, but there's a pretty wide envelope of conditions in which a fast escape hatch is the difference between surviving a fire and burning alive.

The CEO of OceanGate said he "learned the lessons of aviation", but this is obviously BS if he's locking himself in a capsule with flammable equipment, piping oxygen in, and just hoping it doesn't burn. That's a recipe for disaster we know how to avoid.

Currently, even if they could surface, they couldn't get out of the vessel because it's locked from the outside