How is a locked down tablet/laptop in any way similar to a computer with a built-in compiler/interpreter and a full hw schematic available in the manual?
I don't remember getting any compiler or interpreter for Amiga, Atari or Apple Mac. You had to pay for them and the schematics were part of the OS SDK, also commercial.
Also going besides the ROM BASIC or Forth meant buying a compiler/interpreter.
I know the Amiga manuals (Amiga 2000) was very well documented, a friend fixed ours by measuring the various documented points on the main board, finding a poorly soldered component or fried transistor (I forget the details).
AFAIK Arexx was part of Worbench? But yes, you did need to get a compiler/interpreter for that. I thought you were talking about stuff like the C64 generation of computers.
I remember there were GNU tools available for the Amiga, and some magazines came with various development tools -- eg: Blitz Basic. But most were certainly commercial (including Blitz Basic) - but one must consider that even with aminet - there was nothing like the essentially free distribution of today (eg: push to github).
According to this site, Amiga Basic was actually bundled with the machine (note-section: "bundled basic language interpreter (free with machine)"):
