3) Blocking Terrain or a PC (5ft +) on the other side of Grease can’t be jumped over in a horizontal jump.
4) You can’t land in a square of Blocking Terrain.
I'm just going to focus on this part, because you keep missing the point. I haven't disagreed with either 3 or 4. What I've pointed out is that IN ADDITION TO THAT, blocking terrain or an enemy on the other side of grease can't be walked into. So if the grease can't be jumped across, it ALSO can't be walked across, so there's no reason for the 'giants' to try to walk past it. Saying 'ah-ha, you can't jump over this obstacle because there's solid walls on the other side, you'll have to walk through it' begs the question of why you'd want to walk through it if there's solid walls on the other side.