the part in s3 when eddie gets locked in the crypt really highlights how fabian is a sibuna veteran and kt is completely new to this stuff.
every time fabian gets suspicious, kt brushes it off with a comment about how skipping class or breaking rank is just classic eddie stuff - because to her, it is.
but fabian has been involved with (and a victim of) these shenanigans for far too long. he can tell instinctively when something is amiss because it has been too many times, so now it sets his radar blinking. that's why he can't brush off eddie's disappearance like kt can (not to mention, one of his best friends went missing for a full year, only for him to find out she'd literally been kidnapped by a cult operating within the school).
it's not just about him being the most intelligent. it's about him the most being experienced. fabian's spider senses are way too strong to put it down to eddie being eddie (and what do you know - fabian's right).
