I can almost guarantee you that these models will underperform the market in the long run, because they are simply not designed for this purpose. LLMs are designed to simulate a conversation, not predict forward returns of a time series. What's more, most of the widely disseminated knowledge out there on the topic is effectively worthless, because there is an entire cottage industry of fake trading gurus and grifters, and the LLMs have no ability to separate actual information from the BS.
If you really wanted to do this, you would have to train specialist models - not LLMs - for trading, which is what firms are doing, but those are strictly proprietary.
The only other option would be to train an LLM on actually correct information and then see if it can design the specialist model itself, but most of the information you would need for that purpose is effectively hidden and not found in public sources. It is also entirely possible that these trading firms have already been trying this: using their proprietary knowledge and data to attempt to train a model that can act as a quant researcher.