Sorry I meant Spock didn't need to be an engineer to do what he did in TWOK. Just a Captain with 20 odd years experience on the Enterprise.Spock didn't look like he was doing heaps of Engineering calculations in TWOK.
Spock had already done heaps of Engineering calculations in TMP, outclassing the best Starfleet had to offer, manning the brand spanking new ENT refit. The precedent is there.
And if he had todo some calculations he probably could have.