In an ideal situation you may be quicker...but, you have to time the ferry schedule and if you arrive at a busy time you may miss one ferry and have to wait for the nex
Not even in the perfect world is it even close. It used to be closer when 64 was a little 2 lane and the Ocracoke ferry could use the shorter route, but now 64 is 70mph (after Isabell) for a good stretch and the ferry is 30 minutes slower because of the channel filling in.
For example take Beaufort NC which is the closest city to the Cedar Island Ferry and you want to go to Buxton. You can go around in about 4:45.
Beaufort to Cedar Island Ferry Terminal : 50 minutes (But NCDOT is warning that construction on 70 is making this slower and give an extra 30 minutes)
Have to be there 30 minutes prior: 30 Minutes with reservation (do not think of doing it without)
Ferry Travel time to Ocracoke: 135 minutes
Travel time across Ocracoke: 25 minutes
Arrive and load ocracoke ferry: 45 minutes if lucky
Ferry Travel to Hatteras: 55 minutes
Hatteras to Buxton: 30 minutes
370 minutes or 6:10 minutes, which is optimistic.
If you catch the evening ferry out of Cedar Island and have a picnic on the ferry and drink a couple of beers it can be nice and relaxing.