Yeah, being fast paced is the opposite of One Piece... Each arc takes its time and gives all the new and returning characters their time in the spotlight and that contributes to how long it is.
The Idea it would take five years to tell this story from beginning to end is insane to me,
That would be for any other series for me... There's something about One Piece that makes its slow pace feel more rewarding than annoying. (That is the Manga. The anime has even slower pace since the second half of the series and it's becoming very bad! So much, there's a fan-made shortened version of it.)
Chapter 100 (Anime episode 52) of One Piece only marks the end of the prologue after all...