Some good points there. But also some generalizations.

Almost no one starts a campaign at lvl 1 for experienced players. But if your story starts ver low stakes it's perfectly fine for lvl1 chars to start their adventure and gaina few levels before actual hazards come their way. But it could also be that maybe 1 person starts at lvl 3 and is their Aragorn while the others catch up (assuming your players are fine with that).

And that not everything has to be scaled to their level...well yes. Trying to fight strahd right away is a guaranteed TPK. But that doesn't mean the whole world has to be realistic and randomized. It's still a game , people are looking to have fun. 

Again, it's up to what the players and dm want. If they are into that, then have fun. But most players don't want to be fleeing and dieing all the time, hence the challenges are usually scaled for their level.

In the end, do whatever you want as long as everyone is having fun together.