I've spent a year reverse-engineering the BMTH style synth sound in Serum. Here's what I actually found
Bring me the horizon seems to always have this giant wall of synths behind their guitars. But you can categorize them in just three sections:
The Bass. They're using an organic bass together with a sub bass/reese type bass. Super compressed. That brings low-end consistency and if done right, some nice harmonics.
The Mids. They are usually some brighter, distorted sustains. 1 or max. 2 pads are enough. One that sits in the same octave as the rhythm guitar and one that's an octave above. Either same chords or inverted. For the mix, group them and make a sidechain compression: The low-band up to 600 Hz, I would just compress that a lot / before cut quite a bit of that with an eq 6db slope. And the higher band, 600ish to 20Khz, make it sidechained to the rhythm guitars. That way it really comes only out when the guitars are a bit more quiet. Worked insane.
The highs. Especially with the Zakk Cervini style mixing, the higher synths (leads etc.) take on the cymbals quite a bit. In their mixes, the cymbals are so low to make space for vocals and the higher synths.
Happy to answer questions if anyones working on that kinda sound!