This is a good point, but I do want to mention that I feel like in the past 5 years we've had lots of extremely popular packages that hook into Emacs internals instead of rolling out their own architecture.

For example, corfu [0] versus company [1]. Company works with capf, but you can also write your own backends for it (specific to company). Corfu also works with capf, but all backends are capf functions instead of a corfu specific backend.

Another good example is eglot [2] versus lsp-mode [3]. Eglot is actually packaged with Emacs now.

There's also other stuff, like vertico [4] (and others that are recommended to download) versus helm/ivy.

I also want to mention that packages that hook into Emacs more don't necessarily mean that they're better. From my POV it's more like you get a lot more things for free and the documentation you dive into will be Emacs specific instead of package specific. It all comes down to preference.

Vertico/Counsel/Orderless is very nice, but Helm and Ivy are fully featured (I always forget how much Helm has for you).

I use corfu, eglot, and vertico now. I have thought about going back to helm and company, especially since I was very familiar with company's backends for a long time.

[0]: https://github.com/minad/corfu

[1]: https://github.com/company-mode/company-mode

[2]: https://github.com/joaotavora/eglot

[3]: https://github.com/emacs-lsp/lsp-mode

[4]: https://github.com/minad/vertico