[quote=@Samdragonx]
So is there anyone here that would die from a single basic punch? (because of their unique character build, for example)
[/quote]

As the first level guarantees max HP rolls, unless you take a negative Con mod, that's unlikely. However, everyone except a barbarian could die (not just be KO'd) from a crit or a lvl 2 spell that has good damage rolls, unless they have excellent Con. And nearly everyone can be KO'd by a good dice roll on damage.

For example, the spell Shatter can deal 3d8 thunder damage in a 10 ft AoE. A well-placed Shatter at average damage would KO anyone who fails their save if their HP is 12 or so. That's a fighter with +2 Con. At max damage, it would kill most of the players outright and KO anyone else. Lvl 2 spells on CR 1 enemies are not rare.

My concern is less with survivability, and more with the fact that lvl 1 play is simply boring. Monks, Rangers, Paladins, and Druids don't even unlock their primary features at lvl 1. Most other classes don't even begin to be interesting until lvl 3 or 5. And casters get either 2 spells per long rest or 1 per short rest if a warlock. The only classes that are effective are the ones the party has gone with: barbarian, rogue, warlock, and also fighter. Potentially bard and monk, but their effectiveness is limited significantly.