In Storm Front, Harry was already operating at the 'Submerged' level, at least in terms of Refresh. That is actually part of why I prefer to have starting players begin at a lower level of power. A starting Wizard (like Harry was at the beginning of Storm Front), with some reasonable choices in terms of skills, focus and enchanted items, can be a very powerful, particularly if played intelligently. Something else to keep in mind, is that in many of the casefiles, Harry is operating largely on his own. Given what he has been up against, it shows what a full wizard can potentially do.
If the idea is for people to just get a feel for the game, then in my view, having people start out in the same league as Harry would be a bit much.
If the idea is for something other than an introductory game, then having potentially complicated characters would likely not matter so much. While this is my view, it has less to do with the ability to tailor encounters (since Fate is pretty easy to adjust) but rather making sure that the players can get a good grasp of the rules, and what their characters can or cannot do.