There is nothing about PowerShell that cannot be discovered through those 4 cmdlets.
If you frequently need to dig down to .NET you are doing it wrong.
Contrary to your previous assertions, PowerShell was designed for REPL from the outset, and it achieves that much better than any Unix/Linux shell, bar perhaps fish.
PowerShells commands (cmdlets) are inherently rich on metadata. You cannot create a cmdlet without exposing metadata which is then used by the shell to drive automatic type coercion, syntax charts in help as well as tab completion.
It is so intrinsic to the concept, that you'll automatically get tab completion for your own functions, and even for your own script files.
PowerShell was definitively NOT designed as an RPC layer. You claim to "know PowerShell probably better than most people", and yet you are unaware that PowerShell was specifically designed as a hostable engine.
It is hostable precisely because Microsoft wanted to have reusable script engine which could be used in-process (!) in administrative GUIs.
Unlike traditional shells, PowerShells cmdlets share memory space with the host (the shell when used as REPL) because it SHOULD NOT use RPC to manipulate objects.
You frequently use "appeal to authority" arguments, but the substance of your posts gives you away. You are certainly no expert on PowerShell.
I would love to see it in other ecosystems, and the prediction that PS could go open source, along with the recent open sourcing of .NET core and CoreCLR gives me hope.
Cheers!
But personally I find working out command names in powershell much more sane, because of the Verb-Noun pair naming convention.
A shell is a REPL. If your language makes actually writing things in that REPL hard, it is definitionally bad at Shell Stuff. I find it significantly easier to write code in C# and then transliterate it to PowerShell than to actually write PowerShell. That's a disastrously bad situation for a shell.
Yes, I am calling you out. I am challenging you to provide concrete examples where Powershell has less discoverability than bash or zsh. I am challenging you to explain why ISE - an environment designed specifically to combine REPL with script authoring - is "unacceptable".
And please, no more hyperbole or condescending remarks.
I learned Powershell mostly from Get-Help. I can usually figure out where to look for a command based on the naming conventions - essentially (one of x verbs)-(one of x nouns). They aren't always fantastic, but for example, Select-String is a little more obvious than grep.
As for substitutability: this should be obvious. I can't substitute it because it isn't interoperable with literally everything else in the stack. It is Microsoft for Microsoft's sake and incompatible with the rest of the non-Microsoft universe in ways that, it must be noted, Apple did not do; while they have proprietary tools in their environments I can still use it with the bog-standard tools that exist on every other Unix machine I ever touch.