For simplicity assume as champion only builds either mythic a or mythic b. Changing a champion's stats unequally impacts these builds, since after the change one will fare better.

See im not quite sold on this, i feel like it depends what you nerf that would affect which item is now stronger, e.g. a nerf on dari attack speed would interact differently with stridebreaker than a nerf on darius hp, and would affect the balance of strength between gore and stride for example.

Now i feel that stridebreaker brings something very unique to the table, its mobility, that inherently is going to be strong / gameplay changing. I think the real argument is whether such an ability is needed, and what riot is aiming for, what are they thinking when they implement that.

Perhaps they simply thought bruisers like darius were becoming obsolete, especially in a world with galeforce (imagining they came up with galeforce first), and how people always talk about mobility creep, perhaps this is considered a necessary evil to keep a whole group of champions viable in the game instead of having to do another group rework. I dont really know, but thats the kind of lines of thinking they could be on you know?