That's the thing though. The option didn't really work, at least early on, in 2008. BC, VT, Clemson, UVA, GW, UNC. Even duke was more on the talent advantage Bebe and Dwyer had over the doormat team. Johnson did a good job but even then it wasn't an overly impressive showing until we blew out miami and beat UGA, but it took a near entire season to get there. There were flashes, but those flashes also largely centered around the talent at skill positions (like against Duke when Bebe went nuts). Johnson made it work primarily because he had an elite DL to lean on while working things out.
Coaches run their system. They may tailor the playcalls in them to the talent they have (for instance we'll probably be run heavier this year than most), but we're not running an offense that fits the current talent. We're running a limited version of the offense to try and get the closest fit with the talent. The coaches talked up a lot of things in the offseason that need to be taken with a more than a little salt.
You're right that he wasn't option ready from a making reads point of view. However, he was 100% physically ready to do what the option required him to do. Beyond that his style of running compensated somewhat for the weaknesses of the team around him in that he could get tough yards even if the blocking wasn't perfect. His style of running, and the offense being naturally run heavy anyways, made it easier for Johnson to have called runs and dress them up as option plays making it easier for Nesbitt. This year it's possible Graham, for example, has the tools needed to succeed in this offense. but I don't think it's likely that he has an equivalent attribute that will make up for the weakness on the OL the way Nesbitt's power running did. Basically, Nesbitt was damn good in 08 despite not being a great option QB, which he became in 09. I think our QBs have potential to be great QBs with a year of experience, but I don't really see how they will be good this year without the ability make the reads and throws that they aren't used to.