The commands you list aren't too bad because they get quickly learned through use. And "grep" at least is pronounceable and feels strangely apt as a command name.
In general though I think the terseness of the standard Unix commands is a problem, particularly for less often used commands. Even after many years of using them I still get "du" and "df" confused, for example.
"Disk usage" could plausibly be the command that tells you how much space you've got left. Maybe "disk free" doesn't apply quite as well to du's function.
If I was designing them from scratch, I'd maybe call them something like "size" and "space" respectively.
I learned Unix in the mid 80s but it wasn't until sometime later I learned or had the epiphany that grep was shorthand for g/re/p. As in global search for regular expression and print the results. Talk about a forehead slapping moment. Not everything in Unix is immediately obvious.
I always end up using both du and df because I can never remember which does what. Half the time, I also can’t remember their names even and have to look them up.
All of the really frequent commands, I can remember (cp, mv, cat, tar, head, tail, ls, mkdir, rm, grep, sed, and a handful of common programs like package managers and git) and everything else I can never remember and have to look up. I personally don’t like the unix command names, most don’t make much sense to me personally. Sure, I like that they’re short, but I can never remember them unless I use them a lot.
In general though I think the terseness of the standard Unix commands is a problem, particularly for less often used commands. Even after many years of using them I still get "du" and "df" confused, for example.