For me it definitely greatly depends on the roleplay, and the GM in question. Generally speaking I don't think the GM should be the one ICly driving the central story due to the simple fact that they're the one who knows where the story is going, what's around the corner, and if they're not careful can make biased calls without even meaning to. I know I personally would be stuck warring between "could my character have figured this out on my own, or am I over-crediting their cleverness based on what *I* know?". It is my belief that GMs should be pulling the strings to try and orchestrate a story, while allowing the players the freedom to DRIVE it.
I know I was once a player in a very large and long running roleplay called the Orsa of Terminus, and I tend to be a very driven player. So it didn't take long for multiple characters of mine to wind up in positions of influence, but one moreso than all the rest. She was leading an entire group of players. The GM left and gave the roleplay to me.
What to do?
I had my character die to save the other characters, creating a space for another player to step up into that role, while also forever changing the course of the story. I never once regretted my decision to do that.
That said, the structure of a roleplay, the size of it, and how close/compatible the players are can really impact whether a GM can effectively also be your main character(s). I find that larger more open-ended roleplays (like our Epic Roleplays here on Storyteller's Circle) are more adaptable because they feature many main characters. A GM isn't stealing the spotlight from all the players by taking a heavy part in one of many stories. IE in the Chronicles of the Omniverse roleplay, a GM isn't allowed to make rulings on their own stuff, so a GM is free to step into the story as a player in one area, while trusting the other GMs to handle GM matters there.
Conversely small roleplays of close friends can function quite well with a GM as your main character if your GM is genuinely invested in writing a story and all the players can equally sway and influence the direction of the story.