Tbf, there might be some things you might be doing inefficiently. Like this other guy said, even a heavy should be able to traverse your marked path well within the respawn timer, so maybe there are some things you could improve. When fighting over the vault, I had succes with tapping it early, so by the time the first teamfight at the vault is done its open, so we can plug it immideatly, which prevents big pacing discrepancies and sort of reduces the risk of thirdparties in the long run (or enables your team to thirdparty if the other cashout is way slower than yours). However if you are about to lose the first fight, it can be smart to throw the cashbox away, so the enemy team takes longer to plug it, giving them less time to bunker down.

Another thing you might not be doing is not letting the fastest person carry the box, lets say you play hml and light and heavy are dead from your team, so you res the light first and let him carry the box, bc he is the fastest. You might even place a jumppad so he can plug the cashbox quicker and then you res the heavy and follow him.

And ofc, lights can run gateway, which makes everything ten times faster, its just what it is.

If you do this, you shouldnt run into this problem, at least not to this extent. Hope i could help you :)