The web operates in a very different world if you've invested in good tooling. I used to be lead on a modestly sized payment processing back end to the tune of about 100 transactions/second (we were essentially Stripe for the client facing apps at the company). In many cases our monitoring and telemetry let us identify root cause in a matter of minutes. Not saying that is or should be the norm for all web apps, but what we had was not too far off from a read-only debugger view of the back end app's state throughout the request and it was very powerful. Of course for us more often than not the root cause was "the bank we depend on is having a problem" so our knowledge couldn't do much other than help the company shape customer communications about the incident.