We don't know it would be effective.

It would write legalese well, it would recall important cases too, but we don't know that more data equates to being good at the task.

As an example ChatGPT 4 can't alphabetize an arbitrary string of text.

Alphabetize the word antidisestablishmentarianism

The word "antidisestablishmentarianism" alphabetized is: "aaaaabdeehiiilmnnsstt"

It doesn't understand the task. It mathematically cannot do this task. No amount of training can allow it to perform this task with the current LLM infrastructure.

We can't assume it has real intelligence, we can't assume that all tasks can be performed or internally represented, and we can't assume that more data equals clearly better results.