Well, it's not that impressive compared to something like Live or Cubase.
Your point being? "A subpar DAW should be enough for everybody in 2017 as long as it's better than 70s era studio technology"?
Not to mention that you compare apples and oranges. These people did rock, punk and/or jazz, not modern r&b, pop or electronic music that are usually more demanding of a DAW for one.
Second they had tens of thousands and sometimes millions of dollars as a budget for a single record, great facilities with top-notch acoustics, multiple producers, access to orchestras and top-notch musicians, and crazily expensive consoles with people to operate them for them.
Third one doesn't compete against Louis Armstrong era sound but against their own's generation's sound and production techniques.
Heck, the more advanced users end up going with a lot of hardware-based solutions and analog equipment.
There's also another meaning of freedom: freedom from having to care of worry about the platform, and being free to create, because you have a thing that "just works".
For musicians that's more important than "route everything to everything" (for which there are solutions even for commercial DAWs, e.g. Rewire for those that do care for it).
It's all about tradeoffs, but Jack and "freedom to modify DAW code" is pretty down on the list of priorities for 99% of musicians.
Also, a lot of time using FOSS is a choice we make not because of the price or principals but for convenience. I simply don't want to juggle licenses and dongles between home and studio computers, or for that matter be forced to install licensing software that is more or less a rootkit...
But the more essential question is: does it matter?
If one is experimental electronic musician / sound artist, it might be worth it.
But the average musician wants a good environment with the features they need built-in (and easy access to quality third party plugins etc for FX etc), not to tinker (and even less so, in C/C++) with their DAW.
If Pure Data was as mature and polished as Max (which it is not) we just as well would.
If not, those things matter more than openness when you have music to record and work to do.
The problem for me is not superior VS inferior or impressive VS unimpressive software but free software VS closed software.
The problem for most people is good and inferior, or "getting my work done with this" and "this is lacking".
Free vs closed doesn't even come second to most people's concerns, and I'm not even sure it should.
My main problem has recently been "why can't I open these songs anymore" vs "can still edit old productions anywhere, any OS, no need for intrusive DRM that takes over my entire laptop just because Steinberg"