Re: arguably other languages better suited to the modern world
Yes, BBC BASIC was only an improvement on what you got for default on home computers at the time, which is almost all cases were BASIC variants, and most often inferior to BBC BASIC. Hard disks were uncommon even at the time Archimedes shipped (with a floppy as standard), so using compilers were impractical -- you wanted programs to load and run without storing extra files on your floppy or using large amounts of memory for compiled code. It was only after I got a hard disk that I started using compilers on my Archimedes. Several compilers existed early on for RISC OS, including Pascal, which was arguably the most popular compiled language at the time (until C took over that role). There was even a compiler for ML, which is a much better language than both Pascal or C.
So, to look at alternatives for BBC BASIC for floppy-only machines, let us consider languages that runs interpreted without too much overhead and which were well-known at the time. Pascal and C are rules out because they are compiled. Forth was mentioned, but only RPN enthusiasts would consider this a superior language. LISP (and variant such as Scheme) is a possibility (LISP was actually available even for the BBC MIcro as a plug-in ROM), but it is probably a bot too esoteric for most hobbyists, and it requires more memory than BASIC and similar languages. Prolog is even more esoteric. COMAL is not much different from BBC BASIC, so this is no strong contender.
Also, BASIC was what was taught in schools, so using a radically different language would have hurt sales. So, overall, I would say BBC BASIC was a sensible choice as the default language. Other languages such as C, Pascal, or ML, were available as alternatives for the more professionally minded (who could afford hard disks and more than 1MB of RAM).