It wasn't about cost estimation. It was just about over estimation, period. Brad wanted a new game, new engine, he wanted a game that incorporated the best of other games like MoM and Dom 3.....but it's like he executed as a puppet master, pulling his team's strings to get what he wanted done without a ton of direct involvement. (Read his dev logs, it's all "Working on AI today. Oh look at this shiny thing my art guys made!"
The thing about the old games is this: the teams were tiny. There was communication. Everyone was on the same page and good ideas flourished and became great game play. Elemental, on the other hand, had all the problems of a modern, major dev team. Lack of communication, compartmentalization, half-assed things getting green lighted because of time and pressure....topped off with a CEO who had dreams equal to his lack of executive oversight.
Saying Elemental failed because of bad cost evaluation is like saying the Iraq War was difficult because of all the damn sand. I'm in the middle of a 4 day Dominions 3 bender and after two games I still can't get enough. That's the level of fun and quality (jesus, just compare the lore of the civilizations between the two) that Elemental aped and failed to execute.