I don’t know what post it was, but if its any help, horror is more of an element while gothic is a genre/mode/mood (scholars like to butt heads on it), horror would be a madman breaking into your house and slaughtering you–it scares you, its dark and grim, but it doesn’t effect you beyond the scare.
A Gothic would have you anxious over the madman, questioning your belief in such a story, and possibly in God and superstition as a whole, while wearing something elegant in a gracefully lit room, with overtones of love running through that anxiety–the madman still shows up and there may still be a slaughter but there is a chase, there is hiding, there is terror instead of horror.
Compare Crimson Peak to Halloween, or Jane Eyre to any lifetime movie where a girl marries a person with a dark secret. Hammer Horror films were very good at treading the line between Gothic and Horror, as was the original Dracula novel. For another book comparison: Frankenstein is a Gothic, but IT is a horror.
Tragedy is common but not a necessity in the Gothic, it often comes as the price for including the terror. Crimson Peak ends in tragedy (and opens with it, as most Gothics do), but the terror and suspense and questions overpower the tragedy–if you haven’t seen it yet, I’ll tell this much: you leave it excited rather than depressed, there are a handful of questions like melting snow in your hand that drip away between your fingers before you can fully form them, ethereal and haunting visuals wash away the last of the nightmare, and then the credits roll–this is the Gothic, as opposed to pure tragedy where we see Horatio speaking of Hamlet’s nobility as he stands over the corpses of the last of his friends.