Not a well established theory, just an implemented software feature being advertised here.

And its trivially true, that when a method that tries out more hyperparameters and more models, the probability increases that it spits out a configuration that works well for you (the only statement in this that comes close to a "theory").

Weather an implemented software is doing that up to a satisfactory manner for a user, or if it can be achieved at all, is a question in the domain of engineering, not theory.