How the Pilot differed regarding Phineas' personality

I like how both Phineas and Ferb's personalities were handled by the show,

In the pilot episode (The Rollercoaster one, If I'm not mistaken?), Ferb might not have been much different. But Phineas' characterization was unmistakably different than what he would end up with for the remainder of the show,

In the pilot, Phineas had partially-closed eyelids, which I inferred was to make him seem smug and cocky. He also didn't come across as friendly and welcoming as how he usually was for the entirety of the show. His response to Candace when she asked them what they were doing (him replying it was "homework"/summer vacation project), almost came across as him "talking down" to her.

The reminder of the show alters this by having his eyes fully opened, to imply how optimistic, excited, and idealistic he is. And rarely, if at all, was there any malice or ill-intent to whoever he was talking to, if he did say something rude or disrespectful, he likely didn't mean it or the recipient took his remarks the wrong way. P and F, as characters were pretty much personification of the child-like innocence, spirit, idealism, curiosity, and eagerness. Traits most folks forget or outright forget, as they grow older into adulthood. A celebration of that, one could say.

I guess this minor correction in his personality was quite ingenious from the writer's side. Otherwise, he would have come across as insufferable and arrogant to the audience, someone who was that way but still never managed to end up in trouble or face any sort of comeuppance for that attitude. Maybe he would have been like Thaddeus, maybe not as unlikeable and insufferable as him, but ya...except we would have been stuck with such a character as the protagonist.

Maybe the intent for them initially, was to depict/parody real-life geniuses and how much of a jerk some/a decent deal of them were/can be to others (Steve Jobs, Oppenheimer, etc...), maybe they initially intended on him having a character arc where he becomes more humble over the course of the show due to experiences, perhaps?

Usually "genius" characters with personality flaws often get some sort of punishment or lesson that negates them into unlikeable territory - Dexter is brilliant (maybe even more so than P&F, arguably) but he is grumpy, and often times, there's always a "punishment" whenever he tends to be arrogant, rude, or grumpy (and he gets that a LOT throughout the show). Same with Tony Stark. Among other examples.

The show would have been nowhere near as beloved and popular as how it ended up being had they stuck with Phineas' original personality and would have alienated many.