the north side route – south fork using the dollar lake trail, is virtually the same length as the vivian creek trail.
the difference is that vivian creek has a lower trailhead, so you’ll have more gain.
but this gain is front loaded – the first mile is a beast – and then it mellows out. i have daytripped san g more than once (on the vc trail), so i think your idea of summiting from the camp is completely reasonable if you’re in good shape. it’s just under 8 miles to the summit from that camp, with just over 4k’ gain to do.
other plus sides are that you have more/better water sources on vivian, and you also have a better view, as the south fork trail was heavily impacted by the fire.
san g is absolutely nothing like whitney, so i would not let that worry you.
if you have any experience at all, which you certainly seem to, you’ll be fine on the vivian creek trail. there’s a reason why it’s the most popular trail on the mountain after all.