Another thing you really have to keep in mind is what Yoda himself pointed out to Obi-wan before Palpatine was revealed, that "Arrogance" was becoming a more common flaw amongst the Jedi and Mace was no exception. I really think that Mace felt that he and three other Jedi would be more than a match for one Sith, and never even expected Palpatine to respond with such fury, skill and speed.
Overconfidence was their enemy.
The Jedi hadn't faced a true Dark Lord of the Sith in a thousand years (Maul being an apprentice and Dooku more of a fallen Jedi). On top of this, they were going against the most powerful Sith in history. Ep III novel states that the Sith had evolved over the 1000 year gap while the Jedi maintained complacency in terms of their philosophies and teachings. The novel even states that Yoda acknowledged that he couldn't defeat what the Sith had become. Yes maybe Mace and co were a little arrogant but I think saying they were ignorant more describes the situation.