This is sub-optimal but the present day reality -- you would not want to run long running and IO operations on actors on the default pool.
This is why we're working on Support custom executors in Swift concurrency which will enable the "make this actor run on this dedicated executor (e.g. single thread)". This is a well known and established pattern from other actor runtimes to handle such threading requirements, and does not affect the semantic model of an actor runtime -- it just affects the small detail™ of where the actor is allowed to run.