It's certain that having two sets of spares to maintain and, as somebody pointed out to me a couple of days ago, on both coasts, it adds to the costs. That being said, if you have a lower-cost type of ship, usually operation and maintenance costs are also proportionately lower, which could offset the additional cost of having two types of ships in the same fleet. It could or could not. That's something that would need to be looked at in more detail if there was one option that was favoured over the others.
On March 8th, 2021. See this statement in context.