Re: However, on FreeBSD
"Each with some shell/awk/find/etc quirk."
Some diverge more from "what you're used to" than others. The beauty of learning bash and other POSIX-like shells as "baby's first CLI" is that there are just so many that more-or-less follow the same rules. You don't have to relearn an entire CLI interface to get the job done (like moving from bash to CMD.) You mostly just have to internalise the exceptions and differences.
PowerShell is different for me here I think largely because a lot of the tools I got used to using with *nix operating systems aren't there. Chaining also works slightly differently, with the weird emphasis on OO shell structures, there are just some things that require a different headspace. (Linear scripting and I are just fine, but OO starts to wander outside my bailiwick.)
More to the point, some of the fundamental assumptions about system usage are different in Windows versus most POSIX systems. Flat-text configuration as one example. (Though I must point out that more and more I can just feed XML into PowerShell-compliant apps and that works. It’s a start.)
Where I start really getting outside my comfort zone though are programming-language CLI shells. Cshell, Rhino, etc.
That’s all a really long way of saying “I think it really matters which CLI is your first.” You never forget your first, and it deeply influences how you view and interact with CLIs forever. Using something like Bash is grand, because it’s close enough to all the other POSIX shells that you can adapt quickly.
Using a real outlier on the POSIX branch might not be as good; the mental list of “exceptions” to what you perceive as “normal” might be significantly higher than otherwise.
I can’t find much empirical research into the difficulties of learning (specifically) shells – nor the deltas imposed on cognition by different POSIX shells – but there is plenty into similar areas. GUI design – as one example – has had billions put into fundamental research on “how far from what someone first learned” you can stray before they get really uncomfortable or have a hard time. Similarly, keyboard design…even the design of musical instruments.
How much those “little differences” matter amongst similarly structured CLIs really could boil down to “which CLI you learned first!"