Neither. In season 1 a computer graphic does refer to Stamets as the chief engineer, though that episode's writer tweeted that was a mistake. Then in season 2 Reno even says she's been ordered by the chief engineer to assist Stamets. Since season 3, who knows? Reno does outrank Stamets, yet Stamets seems to be the go to guy for all engineering related matters, and even orders Reno around despite being lower rank than her. Even weirder, she obeys her orders, sometimes even without without her trademark snark.
Actually, no. Stamets's lab is stated to be the engine room in dialogue all the way back in Context is for Kings.
Fuller wanted to get away from the format of the main cast consist of the crew roster that went on in the other shows. Though either intent got lost after he left or it was a failed premise to begin with, the main cast ended up consisting of most senior staff positions anyway, just without a CMO or chief engineer. Though, really, even in the first season Culber fit the narrative parameters for the CMO anyway, being the medical authority in the show's cast and he was of appropriate rank to be the CMO. They really should have just made him the CMO anyway. And given how the an experimental propulsion drive is central to the show's story arc, it makes it very odd that a chief engineer has never been seen.
If anything, the Disco writers should have learned the lesson Ron Moore learned on BSG. At first, he was adamant not to include Galactica's doctor or engineer, to do so he felt was being too much like Star Trek. But quickly in the first season he learned they needed a doctor on the show in order to deal with President Roslin's cancer storyline. And while they managed to make it all the way to the final season before getting into an engineering related storyline, and without a pre-established character in that role they ended up treating Chief Tyrol as the ship's engineer, which everyone agreed made no sense, but there wasn't much else they could do at that point.
congrats Trekkies.
