I'm not sure I understand the stat growth. It seems you can only get 5 stat points per level, and the level reaches a cap pretty quick. But there's a lot of items and things that change stat growth, so how does that interact? Can your stats increase after you're already at the level cap? Is there a hidden stat somewhere that reflects both the grown stat and the final stat? Most of these things aren't realistically available in the stage of the game where you're actually gaining stats.
Also, enemies keep getting stronger over time such that it seems a game over/restart is inevitable at some point. This may be related to my not understanding stats.
Growth Stats are visible under the Tab Status and then Secondary. They are % based, because they only increase how quickly you get Exp in a certain Stat not the amound of points you can get. The Limit remains the same. So you basically do a Trade-Off.
To make a very basic example. Let's say there are 3 Stats. STR, DEX and AGI. You would increase one of those 3 Stats by 1 using the specific attack they are assign to 10 times, since your growth Stat for all 3 of them is 100%. Now let's say there is a Growth Item that increases the growth of STR by 100%, while it lowers the growth of AGI by 50%. Now it would look like this:
STR 200% growth so you need only 5 Attacks since it's growth is doubled to increase it by 1
DEX 100% growth remains the same, so still 10 Attacks
AGI 50% growth so you need 20 Attacks to increase it by 1 since it's growth is halved.
So now you will increase STR quicker and you can focus on it more, to make a build around it. The Overall Number of Points remain the same you can get, nothing has changed there. Now to be clear, this is a very basic example just to show how it works. Obviously there are much more Stats and much more things that affect those Stats in the game.
Edit: Also good builds even on the hardest Difficulty work just fine deep into the game.