The mouse didn't become some huge profit center and the economy didn't realign around mouse manufacturers. People sure made a lot of money off it indirectly though. The profits accrued from sales of software that supported it well and delivered productivity improvements. Some of the companies who wrote that software also manufactured mice, some didn't.
I think it'll be the same now. It's far from clear that developing and hosting LLMs will be a great business. They'll transform computing anyway. The actual profits will accrue to whoever delivers software which integrates them in a way that delivers more productivity. On some level I feel like it's already happening, Gemini's well integrated into Google Drive, changes how I use it, and saves me time. ChatGPT is just a thing off on the side that I chat randomly with about my hangover. Github Copilot claims it's going to deliver productivity and sometimes kinda does but man it often sucks. Easy to infer from this info who my money will end up going to in the long run.
On diversification, I think anyone who's not a professional investor should steer away from picking individual stocks and already be diversified... I wouldn't advise anyone to get out of the market or to try and time the market. But a correction will come eventually and being invested in very broad index funds smooths out these bumps. To those of us who invest in the whole market, it's notable that a few big AI/tech companies have become a far larger share of the indices than they used to be, and a fairly sure bet that one day, they won't be anymore.