I don't have a strong sense of whether this is reasonable (I see arguments both ways) but I do think it's pretty strongly at odds with how we treat photographs. There are a bunch of photos on my phone where I unquestionably own the copyright, despite putting in much less creativity than I did for some AI images I've generated.
I don't think it's clear how to resolve this, but I do think that if we are going to protect photos and not prompted AI images, the distinction needs to turn on something other than whether "sufficient creativity" was applied to the input of the mechanical system.
Edited to add: It's probably also worth calling out that the question of whether we protect the work produced by a person's use of mechanical system is a separate one from whether we protect the work of others when it is (in various ways, to various degrees, with various likelihoods) reproduced by use of those mechanical systems.