I have a couple of other machines and only one of them has reduced functionality when using Linux libre (e.g. the on-board Radeon graphics chip needs nonfree firmware for higher resolutions).
Guix and GuixSD makes it easy to use a custom kernel package, so you can choose to use a blobby kernel, if you can accept that.
I've heard this myth before too. Here's someone else's succinct answer to it:
It's a common misunderstanding to think that the Linux-libre project forbids loading non-free modules/drivers by user's request after the kernel was installed. In fact, it's a bug that is very hard to fix due to the way that the Linux kernel itself is made, as Alexandre Oliva, member of Linux-libre project, states at http://www.fsfla.org/ikiwiki/blogs/lxo/2013-11-08-linux-libr... (when answering the question "Is there anything that the project wants to do that it can't do now? In general, what are the future plans for the project?").