Hell, what if he's a psychic alien and he keeps talking to them constantly but because they're not psychics they can't hear him and he just doesn't understand that? Of course, deep down I feel like y'all are probably right- the author is probably only filling his tank with normal crazy instead of premium. But goddamn would it ever be funny if this dude was actually just a fucking alien lmao
The problem is that if Spy x Family goes down a path like "we have aliens in the middle", the feeling is that it will be completely out of tune with the series. If we're talking about fiction, talking about "paranormal activity" is much more plausible in wars than "aliens", because in the case of the latter, the broad concept of alien ends up being completely out of tune. And in the end, if we use the idea of "a simple alien discovering something about Earth", it will give a strange feeling to years of history about the Cold War and espionage.
In the case of Melinda, I think the idea of occultism is valid, because occultism is usually an attempt (often vague) to justify something that has not yet been justified by science in some way. Remember that esoteric astrology, for example, helped in the evolution of astronomical science. The attempt to understand the human psyche led to the sciences of the mind, such as psychology and psychiatry.
This is where Loid's role comes in: as a psychiatrist, he has full access to the person's mind, since psychiatrists' job is to try to understand whether what the person has is a real physiological problem in the brain or something that could be a social sensation that would fit into psychology.
In Melinda's case, Desmond's attitudes seem invasive to her, as if he were actually literally reading the minds of everyone around him. (Remember that Shin from Sakamoto Days also has this ability, and the series about the assassin who owns a small shop came a little after SxF - Shin is a good example of how Anya could be as a spy and an adult in terms of how to use her mind for espionage and combat).
In the series, Anya knows how to use her power reasonably well, but she is not mature enough to do so - just remember that she has problems with overload when she needs to use her mind to read several people or she actually easily absorbs other people's readings without wanting to.
So, going back to the plausibility in SxF, again: the series is based on war concepts. And there have been tests in the past for precisely this type of activity. Unless I'm mistaken, in a quick search, we have the example of MK Ultra (the use of drugs to modify the mind) and the Axis experiments (Germany at the time). In the case of SxF, the project that involved Anya and Bond (and probably Desmond) is Project Apple.
https://spy-x-family.fandom.com/wiki/Project_Apple