I was wondering what the precise timed difference is between having a mod specific to a class's power VS not having one. I have noticed my Nightstalkers Dodge seems to charge twice as fast with just one "Class abilities charge faster when using a Void Subclass." The curiosity is, How many times can you stack this? It's obvious Bungie won't let you stack say... Five "Grenades recharge faster on an Arc Subclass." On a Striker titan with double pulse grenades to drop a grenade every 2 seconds. There IS a cap. The question is, Are you only allowed to use ONE armor mod per category? Or does it stack up to 2-3?
Warlocks can technically have 4 for their solar class if they also run eye of another world. But each mod results in diminishing returns.