I've been thinking about this for a long time, along with considering speed for the offensive criteria. In the end, I concluded that HP isn't a determinant factor when deciding the style of the pokémon: The highest defense stat being higher than the highest offensive stat nearly guarantees that the pokémon will work better defensively than offensively, and the opposite is true, too. HP aids a defensive build, letting you having not that high defenses. But if we use this criteria, by having non-astronomical defenses thanks to good HP means it will have offenses 20% as non-astronomical, tops.
I'm not totally happy about this criteria, BTW, so if someone has a better idea, PLEASE propose it in the process guide workshop topic.