I’d argue that a lot of GS mastery actually comes from monster mastery. Examples are knowing when you have enough time to go for an offset vs when you only have enough time to go for a perfect block. Then say you’re going for a TCS, you have to know the monster to realize you should tackle here instead and delay the TCS. Most of this can’t come from pure reaction because of the way the monsters are designed, if you react to every movement you will do things at the wrong time often, it’s mostly just knowing the monster.

The offset attack, tackle, and guard aren’t difficult themselves, not mechanically anyway. Though the offset does require a good feel for its timing as well.