Umm, no, fully disagree.
You should work for every level you obtain, period.
And getting to level 2 is cake. 3 is not hard at all, and 4 is not hard at all, just takes a little more time. I would expect that same for each level afterwards.
But you want to start at level 10? How about Larian just give us God mode?
I think you are missing the point. The OP isnt promoting the idea of less difficulty or an easier game. He is saying to make the lore/situattion/immersion with the level of the party. Not in terms of difficulty. My suggestion would be that they create a story element that would explain why these seasoned adventurers are such a low level, considering they have what seems like a varied background and high level experience with magical items, and have fame for adventuring. These are clearly not Level 1 characters in any sense. Level 1 adventurers are adept at combat and know a skill or spell or two but in no way have they completed many adventures or have any sort of renown. If they have I believe they would be level 3 or 4 atleast.