Unless you have some very weird use case (and probably even then), that sounds like a bad application of the "keyword arguments bad for performance" mental model.
The reason to use immutable structs is better performance when you use them, not when you construct them - how often are you constructing new struct objects that the constructor performance is a significant issue? And if you are constructing many many thousands of objects to the level it becomes a performance concern, any difference from keyword arguments will be easily dwarfed by the cost of actually constructing the struct in memory.
Also, these constructors ar simply passing on these named arguments to the non-keyword constructors. Anything complex you're doing during construction will be happening in the non-keyword constructors, and those do get specialized to have good performance; these keyword constructors are simply providing a small, simple interface to them, in a way that shouldn't affect performance in any measurable way.
Since keyword arguments don't participate in multiple dispatch, they can't be used for compile-time specialization of methods based on their type. That can be a performance issue in specific scenarios, but I think they've taken that as a general rule and misapplied it here (as I mentioned in my sibling comment). For this scenario, that aspect of keyword arguments is most likely irrelevant.
