GDP growth doesn't necessarily mean any one person will be better off. But regardless, if you, say, build something with the help of AI that you couldn't do before, it could make you money, depending on how much you sell.
The ease with which he can use AI is the same as for everyone else. Therefore he gains no relative benefit and can't "make money from AI".
However, information-retrieval and "thinking assistance" helps everyone at the same time. Asking for summarization and clarification of any (legal or technical) document, finding the right references, and so on. It's like everyone gets instant access to a research department.
This means fewer people are needed for "clerical jobs". Effectively, it diminishes the economic value of memorisation and mechanical information work. But that's probably good a thing.
> The ease with which he can use AI is the same as for everyone else. Therefore he gains no relative benefit and can't "make money from AI".
Not really, people are not equal in output. Some people can use their tools much better than others, like juniors versus master craftspeople. Even in startups we see some succeed while many fail, and while there may be macroeconomic conditions (or otherwise those outside of one's control) for such failure, some still rest on the founders themselves and their decisions.