> On a trivial level this is correct as words mean what we collectively decide they mean.
Correct, and collectively we decided that reselling digital work without permission is indeed theft, just as we rightfully decided that digital goods for the most part are like physical goods.
> a) the meaning has been changed
It hasn't really, digital theft still has the same meaning as any form of theft. Some did try to change the meaning and non trivialise the act based on the fact that digital goods are not like phyisical goods. But that's a techincallity based on the nature of digital goods.
Similarly, AI folks wish to change the meaning of theft based on the false assumption that an AI system "learns just like a human". But that's a false assumption. The software does mimic human behaviour, but we all know that it is neither human nor intelligent (if it were intelligent you'd show it a set of multiplications, and from that point onwards it would figure it out on its own. same with writing stories). Yet some are trying to change the meaning of words to accommodate their view of the world in which software that can ingest people's IP at massive scale, mix it in, and output something that looks novel is somehow similar to human learning.
Therefore the matter is trivial. Software ingestsing digital content without permission, and outputting content made of even tiny bits of the original, is theft. Simple as that. However, that does not mean that AI should be banned. It's how the AI software is fed its data that must be brought in line.