He most definitely was, and that's the crux of his entire arc as a character.
As the Great Spirit, we might be inclined to think Mata Nui perfect and infallible, but he was quite the opposite. While he was noble in that he was dead set on completing his goal of saving the home of his creators, he was too focused on that goal, and that's his primary character flaw.
You might also say he was corrupted, in a way, by his own power. He knew the role he held to the Matoran, and he believed it himself, thinking himself unbeatable. That's why he didn't think twice about creating the Makuta, appointing the Barraki, or worrying about the on-goings of the Matoran.
Once he gets expelled from his body is when Mata Nui becomes a real character. Suddenly he's forced into a world of danger and hardship without the god-powers to deal with them. He has no room for hubris anymore, especially when surrounded by much more capable warriors than he in the form of Akar and Kiina. His character arc involves being reduced to the physical form of what his mind really is, a mere mortal if you will, and finding humility and wisdom in it all.
Granted, this wasn't very well executed, especially in The Legend Reborn where, despite not ever having to really deal with a single problem in his life, Mata Nui is able to single-handedly defeat a Vorax, ice axe Straak, a Scopio beast, surf down a mountain side, master the Ignika, defeat the lord of the Skrall, uncover a conspiracy, and lead a national reformation, all within a week or so of gaining a new body. Which is a real shame, because he had the potential to have one of the most compelling character arcs in all of Bionicle.