Epic has more than a few videos on Youtube demonstrating the animation BP as to the logic used in Fortnite. There is one that shows the migration pathways and from what I’ve seen the use of state machines is used in a limited manner as to correctly stage sequences in a proper manner, like jumping where three sequences are required for a complete jump.
I tried to find it but there is to many now to find just the one.
So yes state machines are used by Epic in their games but to an extent that they are not used in the same manner as I’ve seen in a lot of example files in comparison to new features Epic has added in the years since they did the walk through.
That said with new feature additions like the game play plug in and component preference as to character control will make the use of state machines rather redundant as the means to make state changes. To put things into perspective the manner in which character control is managed is out of date, still, and similar in design as to developing a web page using note pad as to other option that should already be available by now.