I don't think starting at any other level than 1 makes sense as for the majority of people never played D&D. Even if you have, but you didn't play 5e you will be overwhelmed with class knowledge that you lack.
I honestly think Larian did a really good job of pacing the level ups - you get a handful of characters, all low level, you have time to ease into the roles, without being stuck in level 1 and 2 too long. Thinking back to Pathfinder, which I never played before Kingmaker, I was sometimes overwhelmed by the amount of class knowledge I had to learn to use my companions properly. That will be the experience for anyone who never touched 5e. Each level, each class means people need to read everything available to them before they can continue on - and for a good game easing the players into its rules is something extremely important or it leads to frustration. Expecting players to read the pen&paper rules to play a video game is unrealistic and would be lazy design. Not to mention pointless because the p&p is made to introduce players into it in the first place.
The issue to me is more the encounter design and story telling than playing low level characters. With Larian there is no mundane. No first steps to put everything into perspective. If you are new to D&D you get the feeling that Mind Flayers, Demons, Drow, hunting parties from Avernus, Red Dragons and so on, are daily occurances for everybody. Underdark is just the cave system next door children go to play, though maybe a bit dangerous. And yes, you can tell stories like these and each encounter is fine by itself, but all combined are at the point where to me it lacks pacing and there is no feeling into what a normal life would be. After act 1 there is nothing that can surprise you anymore - except elementals, you didn't see any of those.
