new Pendulum Z digimon, which are clearly in the style of the first digimon designs
I feel this argument comes up a lot and people completely oversell it. It is true in some respects but the parallels break down pretty fast.
They have cut back (so far) on armored cyborgs and humanoid monsters. But there really isn't that much of a "return to old designs" going on.
The designs are more of a conceptual throwback than a stylistic one. If you put the new artwork next to the old ones it stands out like a sore thumb, everything from the shading, the common proportions and the amount of detail is completely different and you really can't get from point A to B without taking those two decades of evolving designs into consideration.
Yes, we're back to "Variations on animals" but the approach has changed over time. You look at the earlier animal based Digimon like Birdramon, Coelamon, and Hanumon for example and you see that the designs are made monstrous only in a very limited way. Of course there's stylized, more savage looking anatomy, and there's more fantastical influences but they were very straightforward and obvious, focused on very common associations and generally non-organic design elements like weapons clothing and armor parts were used sparingly unless it was the whole point of the particular design itself. Likewise, mutants and monsters based on more fantastical concepts were always more varied but that was their
privilege thanks to their source.
But by now, designs have grown much more detailed and busier looking, references can be far more obscure and I do like that development, the simple stuff would just have become redundant after a while.
Anyway even if we take a look at one of the plainer designs of the set, we can see that progress. Take Tobiumon for example, for modern Digimon standards, an extremely straightforward rendering of a flying fish, but even he has Organic missiles metal armor and big humanoid arms. If we look for this sort of Design among the animal Digimon in the original Pendulums, the closest we get is Pukumon.
And that's exactly the point: Those designs have a level of complexity and "weirdness" that back in the day was reserved for Ultimates.
And again this sort of "complexity" creep is natural, and it is fascinating how concepts evolve over time.
For example, I think Armor Evolution played a part in introducing more layered and more accessory based designs into the lower levels; Many of them were animalistic but they were inherently "layered" designs because besides adapting some animal or other design into the monstrous they also had to include stylistic references to their Digimentals. That meant a lot of, well... armor, insignias, and generally themed details a lot repeating continuous design elements even between different species, all to a degree that wasn't that common before.
And they were a big batch of designs too. So when they were introduced into the general design pool of Digimon, future designs needed to match them even if they didn't have the direct stylistic influence of the Digimentals behind them.
So over time we got designs packed with more details and more specialized themes allowed for more niche visual references and so on and so forth. And with the Pendulum Z Digimon we are getting an interesting meta aspect in that many designs reference earlier Designs without being explicit sub-species.
Long story short, arguing that Pendulum Z "goes back to the roots of early Digimon" is missing at least part of the point.
It's like saying the VW Beetle produced since 2012 is
the same as the original Beetle from the 30s; Even through it's a throwback in some ways, if you actually took it back to that time period people would be looking at you as if you were driving a spaceship.