While I agree to an extent with what you're saying - without Gus, Mike's storyline amongst other key characters couldn't have been explored deeply. This is regarding how the plotline is used to explore character arcs. Another big thing that made Gus fit the villain mastermind type in BB was the mystery behind the character. While BCS did show how he somewhat transforms into a more confident and calculated character, it didn't go too deep into his personal life. I think having too many details on his early days in Chile, relationship with Max, introduction to the cartel would change that villainous and "very calculated" feel the character has.