Theres a lot of threads raising this question and everything in relation to it (and one on the first page of this General) so there really wasn't a need for a new one,... regardless -
Levels 5,7,9,11 are huge powerspikes which can't be properly gauged through discussion here as BG3 is far from the PNP D&D as far as story goes (which campaign ever started pitting the players against a devil commander and his cambions in a mix with mindflayers aplenty) in my opinion Larian will nerf the experience yield even further for Act I come full release, what fun is there in an instant OP party? Our road to Baldurs Gate would be a breeze, highway bandits and random beast encounters would pose no problem (maybe if they buffed their health to insane amounts, but thats just tedious, not a challenging experience), let alone the encounters we will have in the city itself... if they had any form of a sequel planned it would work better in a DLC expansion than a fully fledged new story instance and even that would probably be a minor increase in the level cap, maybe like 1 to 4 levels maximum.
After reading up on the whole ordeal both in the form of peoples inputs on the forum and 5th edition ruleset I will honestly be surprised if we will be able to go over level 13 in the full release of the game, seeing as how our party of misfits would be regarded as fully fledged champions of the realm when the story wraps up. I don't see how they would justify a new start after the end of this storyline. You can't really go back to fighting random mercs and goblins when you're known throughout the lands as a hero that saved everyone from the end of the world, no? Do I have it wrong? Whats the next step - bringing down gods? Becoming a god at level 20? Its just silly. Both from gameplay and story aspect its just hard to implement truthfully.
Who cares? We will use lvl20 mods.
Also this. Someone who wants it will be able to get any level he wants, surely. Even if it breaks the game.
edit: also when they implement Multiclassing the balance of the gameplay will come into question. I don't even want to start thinking about that topic derail.
