If Vulcan possessed a one gravity surface gravity, Spock would have the same strength as a Human of the same size and muscle tone.
Not really. Chimpanzees evolved in the same gravity we did, and are generally no larger than us at most, yet they're typically somewhere from 2 to 4 times as strong as humans. Their muscle fibers are longer and more densely concentrated, so they can generate more force with the same amount of muscle. Muscles can have differences on the inside that aren't evident on the outside.
So yes, gravity is one
factor that can influence a species' strength, but it's wrong to assume it's the only
factor. Species here on Earth can have widely differing strength levels, so the same could be true of species that evolved on planets with gravities close to Earth's.
If anything, humans are toward the low end of the curve when it comes to physical strength. This is partly because our muscles have evolved to favor finer motor control and precision at the expense of raw power, while chimps' muscles tend toward the opposite trade-off
. But it's possible that muscle tissues on some other planet, such as Vulcan, could've evolved yet another type of internal structure that allows both strength and fine motor control. We can't rule out the possibility that it would've been in response to higher gravity, but it didn't have