My shark doesn't look as smooth as Kent's, is it that I'm not smoothing enough with the smooth brush or remeshing enough or something else?
I'd say it has more about to do with the level of detail. In other words, you have less polygons and thus bigger faces. Kent probably has much more detail and smaller faces and it makes it look much more smooth. I can see in the video the faceted faces in Kent's model, just not as much as yours. But it's not a big deal, you don't want to make it overkill and your mesh being too dense. You can try right click and shade smooth.
I agree with Omar - especially the bottom lip could use some additional mesh resolution (more polygons).
The balance lies in having enough polygons to appear smooth and achieve your shapes; not too many polygons, nor too few. With an appropriate mesh resolution, it's still an art (and discipline) to gently polish all the bumps and divots of a sculpture. It's kind of like the aluminum ball challenge.
It will never be perfect unless you retopologize, so keep your expectations in check. And FWIW you're doing quite well with surface smoothness quality. I've seen much worse submitted to this exercise.
I feel this advice is never satisfying, but keep practicing and I think you'll naturally get better and better.
i ran in to the same problem, turns out i had cavity on and it highlighted everything, it looked a lot smoother without it, i also remeshed 1 extra time, i might also apply smooth / autosmooth at the end
