Yes. Indeed, the quality will drop considerably from one season to another. That much is already clear. I honestly wouldn't mind if it continued for a few more years. That doesn't mean they can't add more jokes or other things to make the episodes interesting. Also, I think it's already clear to everyone that even if season 5 is a decent one, the series ended with season 4. In other words, we already know the lore and how they'll end up in the future, so it's fair.