I oversimplified it on purpose because I'm not sure where they are going with this game as far as level caps and such. The DC difficulty table you laid out works fine for D&D campaigns that result in a level 20 party of 4-6 players but, from what I've seen from the game, it wouldn't work out so easily in BG3 for a few reasons such as the 1 try limit, reduced party size and bonus caps. So far, my stats have been maxing out at 17 and I haven't seen a way to increase them any further in early access. In normal D&D, the max limit on a stat is 18-20 depending on the DM and campaign so hitting a 25 or 30 with feats, expertise, racial bonuses, class bonus, background bonuses, inspiration and the like are all possible. However, I am not aware of any mention of feats, inspiration or even stat boosts as you level up in BG3 so you can't use traditional D&D logic.
