Ace wanted to sail the world to prove himself. He didn't follow no shit, he had his own reasons as well as Sabo had his. Go read chapter 585. Got your answer?
This second paragraph of yours, my lord... Better character is about the writing, a character who seeks for approval can be better written than one who seeks for freedom, just like Ace and Sabo for example LOL, when will you get that?
Imagine thinking a character is better than the other for his believes, even though his character is all around lazy writing and plot conviniences?
Again, I've already explained to you what Ace's character is about. He giving up in being the pirate king and wanting to make WB instead isn't a signal of bad written character. You need to understand this first. You can say it is a signal of weakness, I'm ok with that, but weakness doesn't make any character bad. If you think otherwise go and create a Gary Stu then, let's see how that plays out. Ace's ambition, his TRUE ambition, was to answer this question: did I deserve to be born? And he didn't find the answer to this question as a captain, but he found being a WB pirate. See how he giving up in trying to be the pirate king isn't a signal of bad written character at all? Rather the other way around?