Not the parent, but I think their approach is the correct one even though their line that you quote "You can't debug something..." should be everything instead of something.
The issue with your juniors is them throwing their hands in the air without actually reading the code when they hit a wall, and not them trying to reproduce and inspect the bug first.
What's the issue with telling them, "Obviously if you can't reproduce it and inspect it with dev tools, read the code."?
I've won bets off devs who blamed me cause they said they couldn't reproduce the bug consistently when they tried but it would happen randomly in production. Mind you, the bet wasn't even about who was at fault. The bet was that I could reproduce it if I actually tried.
You are complaining about juniors in a role that's known for the motto "it works on my machine" of course they're going to whine the moment it takes some effort to reproduce something.
At the end of the day, how are you going to claim you fixed an issue if you can't reproduce it to begin with? The senior has to now read the code more carefully cause there is no proof the junior actually fixed anything.