How much custom DSP is expectable in commercial plug-ins?

I used to think that unique products should have unique technology, but lately, I’ve thought that the commercial nature might well mean that most companies would actually not invest in customization, but simply leverage common, well-known C/C++ libraries, and perhaps add a small custom modulation bit or maybe just try to make the GUI very nice.

Camel Audio Alchemy for example is said to have been developed for four years, and it has 31 filters. But I didn’t think they were all developed from scratch. Especially when I think that most usable filters have already been invented, which means that designing a new filter should be a very demanding task.

I wonder what kinds of practices exist w.r.t. FX in the industry?

Do companies develop their own libraries by mixing public libraries and their own ideas?

How much straight public library stuff could one realistically expect?