There is some bad math here. I don't know if future games are listed in Vegas yet but if I had that info we could get a real accurate win percentage for each game. We cant just arbitrarily make up numbers and expect our percentages to be even close. The spread is really accurate at depicting the probability of winning each game.
Once we have that info it is much harder to predict the chance of playing in the title game and winning it all. There are two reasons why vegas odds are much more optimistic that anything that has been listed on this site. First, it would be dumb for Vegas to list the actual odds because they know stupid bettors will think osu at 7-1 is a steal when in reality it is much closer to 20-1 to win it all. Vegas just prints money on these future bets. They are probably the most -EV bets in Vegas. Second you will need a database to run a monte Carlo simulation to determine what percentage of the time OSU gets in the title game if they have 1 loss, or even possibly, 2 losses. Any percentage we calculate on here isn't quite close enough because there is a decent chance OSU gets in with one loss and that is pretty hard to account for because that depends on Bama, Oregon, OU, Florida, etc etc.