As I see it it is a bit like every new DM or Group you start playing D&D with as it is not an MMO, you can lay down some basic agreements with the people you want to play with. Some DM's are more forgiving with what they allow, some are less, some players are just Maximizers who want to be halfgods, some prefer a style that is more focussed on roleplaying. Myself I like to give my players some wiggling space for creativity even if it is against the rules, the rule of cool trumps the Book. So, as I see it, Larian caters to this possibilities, as the players can choose how they want to play the game. There's a certain possibility of conflict and discussion but letting the players "police" themselves is not necessarily bad quality, but, dare I say it, a more liberal approach to the fact that there are countless different type of players and styles of playing. A group of Teenagers new to the world are playing differently as a bunch of veterans who have decades of experience under their belly and that is ok as it is. They allow flexibility to your style and that is not a bad thing.
Yes, but there's a limit to the amount and quality of changes that can reasonably be made, particularly if the pitch to get people to join is "We're playing a game based on the D&D 5e ruleset (and you have to pay $60 to play)."
Some wiggling room for creativity? Fine A bit of rule of cool? Fine Making drastic changes to the system that invalidate entire builds, increase the power of already powerful builds, all under the guise of "well, I'm not banning any specific build, so you're free to play a suboptimal character if you want - others just might have all of your abilities and more"...I would not play with such a DM.
Also, there are already rules for multiclassing in 5e, which allow for the flexibility you're advocating for. With Point Buy, you can get at least a 13 in all stats - enabling you to multiclass into and out of any race! So Larian hasn't really added any flexibility - they've just massively increased the power of such builds.
