It's not specifically about the time lost, but setting you back 30+minutes doesn't make you improve in persona. If they wanted you to get better, they'd let you be immediately back in the situation where you messed up and force you to reconsider what you did wrong just then.
So how is that different to any game ever if it isn't about the time lost?
* TW3, ride for 20 minutes, burst into a fight you are not prepared for, die. Go back 20 minutes and get asked to ride again through the same boring landscape.
* Mario, fall down a hole at the end of the level, get sent back to the start of the level. You could have used the midpoint flag, but of course just like in Persona 5 people will apparently see it but forget to save their progress. Should they instead drop you back on the other side of the hole to try again?
* Assassins Creed ... oh right you can't really fail, just try again until you get it right and we'll automatically make it easier for you each time too.
Guess which of those three games is utter garbage. Persona 5 has a fail state, this is true. If you fail, you get to play that part of the game again, this should actually be a joy and in P5's case it is.
So the only real thing you can question is the ratio of failure to replay time. Some people might argue this is too high in P5 because they don't enjoy battles that much. This is fair enough, but is opinion, not something that needs to be changed as a wrong design and there are already difficulty levels included to take care of it.
I'd also suggest that the people really complaining, those losing "an hour," are following a guide and trying to clear the first dungeon in one day. You should never be losing that much time if you are playing the game normally.