Laurence would be a lot more expensive, I assume the budget for this version was far less considering how it was released and almost cancelled mid-way (see below), they had a good reason plot wise to use someone cheaper, and perhaps there was something else behind the scenes no one wants to talk about publicly.

That said, I agree that using Laurence would have been better as a viewer.

It didn't really serve any meaningful purpose.

One of the characters in the first part of the movie explained the purpose and to me it made sense.

Overall I think they covered all the bases well regarding plot twists and why things were done. Especially with Thomas not wanting to do the 4th iteration of the video game and blaming Warner Bros, which was Wachowski's sentiment on making this movie.

Wachowski tried to end this movie before it even finished (blaming COVID from what I recall), but the cast themselves were able to talk them into completing it.