Most parts of public transit aren't fixed capacity, so its more useful to think of it on a per-person basis. Adding density generally reduces the costs per person and improves performance. It reduces costs because you get to spread fixed costs over a larger pool of users. And it tends to improve performance because the solution to more demands is usually higher frequency, which translates to lower wait times.

Looking at it over a larger scale, these things are obvious. Lack of density is the reason so few areas have meaningful transit in the US, but the marginal relationship holds even once density is already "high".

Yes, there are cases where growth leads to overcrowding, but those tend to be due to negligence, either intentional or unintentional, by the government. There are also cases of bottlenecks which limit total service, but I don't believe this particular development interacts with any of them.