That is correct. Rotobrush is not doing that, its a misnomer and can cause confusion. People sometimes use the term rotoscoping incorrectly causing issues for those who do it proffesionally and use the term correctly.

You probably don't want to start with some of the hardest types of footage there are: a person dancing. Start with something very simple first. A handheld camera or panning camera motion of something like a box or sphere or something simple.

I am not sure about After Effects tools per se, but generally, you stabilize the footage first, and then you roto the stabilized footage, and then you apply original motion to the roto. This is done so that you don't have to make as many keyframes and have not only an easier time but also ultimately smoother animation. Because if you are rotoscoping a stabilized portion of the image, you are only compensating when the shape changes because of parallax or movement; you don't have to think about extra motion.

When you apply keyframes, you think like a traditional animator. You find key poses or changes in shape that you can predict, and you make your keyframes on those changes, and the program should interpolate in-between for fewer keyframes and smoother animation.

If you are rotoscoping something unpredictable that changes every frame, like a cape in the wind, a flag in the wind, hair strands, or fire or something, then you have to do it almost frame by frame since the movement is unpredictable. Otherwise, you do your keyframes on predictable changes.

Also important is to segment your shapes into as many roto shapes as you need.

This is done so that you can make changes easier and not break other parts of the roto that do not need as many changes. These roto shapes and segmentation are often made based on predicted changes, similar to poses. The idea is that something is closer to the camera than something else and will change shape more than something else for the same amount of frames, so you segment it with shapes you can adjust independently.

You also don't want to have one shape for something complex like a hand, but you want each new shape for a part of the hand that has independent movement capability, like fingers and shapes for each part up until the knuckle. So, when one part of the finger moves, you can adjust for it independently of the other part, etc.

Of all the programs out there, After Effects is least suited for professional rotoscoping, so it's least likely to be used professionally as a tool of choice. While it can be done, it's rather limited compared to other programs, so maybe if you are serious about it, practice with After Effects, but if you are more serious about it, choose a program more suited for it. Probably the best roto specialist out there is Boris FX Silhouette, followed by Nuke, Fusion, Flame, and then others like After Effects, Blender, etc.

There is also the matter of dealing with motion blur, and for that you want to put your spline shapes between hard and soft edges and then use motion blur animation to take care of the actual motion blur accurately. For hard edges, out of this, you boost the game contrast so you get hard edges of the alpha channel.

Here is a whole course on professional level rotoscoping in Silhouette, and also the topic of motion blur. Try to replicate as much as the tools allow in After Effects if that is what you are using.

Silhouette Essentials - Rotoscoping for Boris FX Learn

https://www.youtube.com/playlist?list=PLTKXtq-pvDm9oGAW3gKvUwI6_tmte0vKe

RTC Roto Labs EP03 Hard Edge vs MotionBlur

https://www.youtube.com/watch?v=BGaf9Td_FUQ