I am a fan for the zero to hero model. I feel having that early campaign part being more realistic and gritty helps set the proper contrast for when they gain in power and become heroic. It's like that saying, you can't really appreciate something fully unless you know what it's like without it. Additionally, it provides different challenges from the start of the campaign to the end of it, where many problems are easily solved through magical means. It keeps the game from being the same thing over and over, IME, when the players have variation of problem solving challenges rather than "super power" for everything.