I want you to pour a stiff drink, find a comfortable chair, and call a friend for moral support. Because I'm about to scandalize you.
There is no cheating in advertising.
But Kiva, what about tracing? Tracing is fine. But Kiva, what about copy+paste? Also fine. Textures? Fine. Filters? Fine. Reach under your chair. Everything is fine!!!
It's okay to use the tools that are available to you. If it makes your work better and/or (more importantly) faster, it's okay to use that tool. Be shameless. Be free. Rejoice like a hyped-up baby goat with no sense of impostor syndrome. Because this isn't the Olympics, there are no judges to police your performance-enhancing Photoshop-shortcuts. With the exception of plagiarism, the world is your cheating-oyster.
That said, sometimes there's no photo reference to trace or 3D model to orient you. Or that, due to copyright reasons, you can't use what is available. In those cases you're left with whatever talent and skill you have in your arsenal. You may find that under those circumstances your work doesn't hold up. That's really the only risk posed by using a lot of shortcuts. Sometimes, there's no shortcut available.
Years ago I was chatting with an old timer who's an absolute legend. He was sketching from reference but wasn't tracing one of the faces which he easily could have. I asked him whether he ever traced to speed things up. He said, "No, because everything I trace looks really good, but then everything else looks worse by comparison." To which I replied, "The trick to tracing is in not doing it very well. Then it all looks the same." We both laughed. I was making a joke–because honestly–there's little I could tell him about art that he couldn't have taught a semester on. But that joke did get me thinking. And there is some truth in it.
My advice: Trace poorly
If I trace the proportions of something but my line work isn't married to the reference image, I find it easier to incorporate that traced component into a larger composition. Basically, I trace it poorly. The lines don't match up with the outlines or details of the original. But they do convey a feeling of movement that better reflects the composition as a whole. When it comes to copying and pasting, similar rules apply. If you put a little work into changing the size, angle, and occasional detail you will avoid being caught out as someone copy+pasting their way to a fleshed out scene. All artistic pride aside, if your shortcuts are too obvious you run the risk of viewers becoming distracted by them. I think that's why tracing, copy+paste, and filters like cutout are so stigmatized–because some of the end users can identify those tools. And no one wants to know how the sausage is made. Can you imagine people out here saying, "Real artists don't re-size or rotate parts of their images', or "Real artists aren't using ctrl+z to undo a mistake". Nope, because that sounds patently absurd. But those digital processes are about as "unnatural" to traditional artwork as any other. They just happen to be undetectable in the finished piece. So create a new layer, 68% transparency, select a brush tool, and rip that sucker off.