Politics is a bit biased, not only because many of these people don't write their own speeches, but also because the complexity of what they say is not neutral. Simpler speech conveys the idea of being no-nonsense and close to the people, while more complexity gives the impression of being intelligent and well thought out.
Depending on who you want to target, you may go one side or the other. For example, republicans tend to use simpler words than democrats to match what their electorate value.
Re-watching Bush Jr now, in Trump era, makes Bush sound like a veritable genius. And we thought then that he was stupid (and in comparison to himself from a decade or two earlier he was)
In his first term people were suggesting that he's functionally illiterate and is incapable of following even the teleprompter. Whether that or he always thinks he's smarter than anyone so wouldn't follow the teleprompter written by someone else.
Depending on who you want to target, you may go one side or the other. For example, republicans tend to use simpler words than democrats to match what their electorate value.