Gary isn’t just a hacker, he is an oracle, it’s the expression of his minor talent, allowing him to predict the future from the scant information available. That means his talent is magnified by the Information Age and is complimentary to technology rather than antithetical like a wizards.
Yes, Marcone and Lara have their own people, it didn’t stop him spying on Thomas and Justine, covered by Lara’s people so presumably he is also in Marcone’s System . Ironically if he is monitoring practitioners, he may have already caught onto Marcone before he revealed himself to Harry.
The Faerie Courts are in the Never Never, but Molly has a phone, he’s probably in that, same with Fix, so he has probably penetrated that part of both Courts in the mortal world ...
I think it
likely that Gary has some sort of "oracular" or "ultra-intuitive" ability, but you are describing something WAY more than a "minor talent!" (Also, I don't recall any in-canon "reveal" of Gary-as-Oracle (though I haven't yet gotten the last few shorts); is there WoJ on this?)
Hacking the Summer Knight , and the Winter Lady? You
do realize that one of the things faeries are
really good at is knowing hidden things, right? If he's stepping on the Faerie Courts' toes this way... then Gary is a
major talent, not a minor one! As a side-note, though: what exactly do Sir Fix and Lady Molly
do with their phones??!? Dollars to donuts they don't interact with distant members of their respective Faerie Courts. I bet that mostly, they do mortal-facing stuff... and
not as Faerie representatives.
Goodman Grey uses his non-descript face way too much, the human eye passes over it, facial recognition doesn’t. His car doesn’t shapeshift. He is a dedicated gamer, that’s one way to get to him. He can and does use e-mail, which means he has a phone capable of being hacked. It depends on how good his assistant is on whether they can keep Garry out. My bet is he is being monitored by Gary through his gaming, it’s the one thing his assistant is dismissive of, so Grey likely also has a portable internet capable gaming device with apps which have back doors Gary can exploit.
Goodman Grey is a
shapeshifter. Facial recognition loses him entirely, each time he shifts. He can turn into a bird, or a bat, and fly; he can turn into a rat, and climb through drains.
Also, both general cctv-based monitoring, and facial-recognition tech, are well-publicized but highly-imperfect. I expect Grey knows both the tech & its limits, and has established ways to escape the surveillance. Tech may be Gary's expertise... but passing unnoticed is Grey's.
I am unclear how much Grey might overlap his "gaming" devices with his "professional" devices, but it's not all that hard to create wholly-separate online identities, and keep them on different devices.
Again -- Grey's talents are highly-unusual and highly-specialized; Vadderung suggested there were only a half-dozen or so in the entire world. Your theory calls for Gary to be able to out-perform Grey
in Grey's own area of specialization... if that's so (and maybe it is; but I doubt it) it shows Gary as a major talent.
OTOH, maybe he isn't that careful... The GG short
Monsters is still on my to-track-down-and-read list, so any revelations there aren't yet on my own radar.
(n.b. the Archive is a major oracle, of the sort you describe; Ivy listens to calls on Molly's phone, almost certainly!)