On the one hand, I tend to agree with you. I used LaTeX (with beamer) to make several slideshows over the past few years, and it seems safe to say that this is not the exactly the kind of thing that plays to TeX's strengths.
On the other hand, there exist wizards who do things like this:
(check out the pink one with hearts; note that it uses random numbers so it doesn't even come out the same way each time, try doing that with anything but TeX (just don't ask why you'd want to); there's also one other that also used random numbers)
That page’s examples are mostly a bunch of paragraphs of prose (that part, TeX is great at), some with fancy formatting that took significantly more effort than the equivalent effect in InDesign or QuarkXPress. The one with the Zapfino doesn’t bother using any alternate glyphs (arguably the main reason to ever use Zapfino). A few others are vector graphics projects that would be best done in Illustrator, Inkscape, or similar. As you go down the list, the examples (like the thing with the hearts) start to be examples of tacky overwrought things slapped together by amateurs.
Obviously TeX is an extremely flexible system, and it’s possible (fun even!) to use it for all kinds of purposes it wasn’t designed for. Analogously, it would also be possible to write a web application in assembly code running on an Arduino. I said it wasn’t a very effective or productive tool for the job, not that it wasn’t possible.
What I meant to say was that in the hands of the right person, it would be effective and productive, but since you're not particularly convinced by anything on that page, I think I'll have to concede this point. You win :)
On the other hand, there exist wizards who do things like this:
https://tex.stackexchange.com/questions/134638/showcase-tex-...
(check out the pink one with hearts; note that it uses random numbers so it doesn't even come out the same way each time, try doing that with anything but TeX (just don't ask why you'd want to); there's also one other that also used random numbers)