I think this obliquely gets at one of the real and fundamental problems with the game, which is that success is taken for granted. Running into a monster that is out of your league should be fun and thrilling, but a combination of play culture, linear adventures, and rules that don't really inject much surprise or nuance into proceedings, all mean that the game isn't really able to handle situations like that.
If you go back to 'classic' editions, stuff like reaction tables, encounter distance rolls, and rules for escape and pursuit meant that running into a manticore at level 1 wasn't necessarily a TPK. It doesn't need to be in 5e, either, but I think most players have been conditioned to assume they should fight every monster and win every fight, and there aren't any rules to guide them toward other outcomes. It doesn't help that 5e puts a huge emphasis on every PC being an important and special hero, but doesn't offer any stakes for a loss other than death.
Skilled groups can overcome most of this, but it's a terrible introduction to the hobby.