That's what patents are for. These "knockoffs" aren't copying some technology, they are copying a style. It's not like ADA spent months running flow optimization simulations on their filters and lily pipes (assumption, but let's be honest...), only to have someone copy their exact specs. Now, if someone copied something like the Spin pipe, which may or may not have a patent, you could make that argument
Actually they did do something like that.
Almost all of their products have had a TON of R&D put in, seriously they rival Reef products like Vortech in this regard. The Solar series took 10 years to develop after an in depth study of lighting patterns and spectrum in the Amazon river (yep, straight to the source). They are not the gold standard for nothing. Back to the Lily Pipe series, they tested flow patterns to find which shape was the optimal one for use in a planted aquarium, one that would provide good circulation across the entire tank and not disturb the substrate or plants too much. This concept holds true even on large 180g where they use 1 set of pipes and have lush growth still. Then to further refine the design, you can raise the pipe to lower or increase oxygenation of the water. Finally they subtlety incorporated a element of Wabi Sabi in the product, when you raise it up it sounds like a Japanese creek or stream. The genuine P-6 Lily pipe is one of a very limited amount of products that impressed me after purchase. Pictures on a website don't do it justice, only once you purchase and use their products do you fully understand the hype and popularity. It is not because they are gimmicks, they are fully functional and aesthetically nice, form +function. If you are careful cleaning then the two downsides (algae and breakage) disappear and you are left with the perfect outflow. ADA further innovated by making multiple designs for use in different tanks like a Poppy (gentler), Violet (faster), Spin (nano) and stainless steel (durability) pipes. At least Cal Aqua tried to do something different with some of their glassware after the fact, but now loads of brands are knocking off what ADA created and popularized.
Ps: Sorry for going way off topic, last post regarding it. I just like everyone to have the knowledge and information available to them.