@Lensing I could totally believe that it's based on intent. My personal opinion is that I have not experienced reading many stories that follow this format, but it seems to be a popular choice for manga where the mc is just for a reader to self insert.
Maybe it depends on what kind of story you're crafting and who you are aiming the story towards. I think if I were crafting an escapist fantasy I probably wouldn't go out of my way to have the MC be too unique.
@VersusVII
It does seem to be that a character with strong goals is part of giving the reader a series of questions to seek answers for and therefore care about.
Some people are really torn about Breaking Bad and particularly Walt as an evil character because, well he's evil. Sometimes people need to resonate with a main character on a particular level like, they need to agree with them on a value based level. I am a lot more distant, it matters more how they are connected to the tale they are woven into and learning what will happen next because of their actions.
@TheLemmaLlama
You know, I can't help but feel like readers falling for the side character as opposed to the main one is pretty common. This is just me speculating, but I have to wonder if in situations where the main character was written as an audience surrogate a 'little too well' then the portion of viewers looking for something more would gravitate away from the MC. As a result of side characters not being written explicitly for being a self insert, they end up more developed and unique?
For instance, if your main character is super heroic and self-sacrificing, never hesitating to put themself in danger to save people they barely know, please dear god explain why they are that way, most real people I see in my everyday life do not behave that way and I need reasons :'D
Huge. People always have a reason for doing something. "It's fun" and "I felt like it" are just as valid as something overly complex and it doesn't always have to be needlessly complicated. There's a time and place for giving a character a "reason" and a "damn good reason".