But, as I've been saying, you won't need to use the Fighting move often, or even at all. That "fear factor" your describing is why using a special attack such as Dark Pulse is so deadly, not the reason why Focus Punch is. Plus, I would rather not use a -Defense nature on something that can take hits like Tar. You say he's so weak to these physical attacks, but he usually survives an LO Waterfall from Gyara, and LO Bullet Punch from Scizor (no matter what I do I can't make Tyranitar take a fighting attack sorry). Tyranitar has great physical bulk and despite his many "physical" weaknesses, he can usually survive those attacks you mentioned.
HP Grass is a good thing to pop that Swampert out, but its usefullness extents to Rhyperior, which is gaining popularity. Additionally, HP Grass is your strongest attack against most grounds if you forgo Ice Beam like I suggest, and if you decide against Thunderbolt it becomes your strongest move on the likes of Vaporeon. Earth Power allows me to keep my Modest Nature, and murders Heatran, and other steels just as well as Flamethrower. I've always disliked using special natures just to accomplish one feat, and it is extra important because Tyranitar needs his jump on Skarmory alot of the time, and can take physical hits quite well, despite what you say. The set is a suprise value anyway, so this splitting my nature has less of a value than it does on say, Choice Band Salamence (i disagree with that too, but thats for a different thread) And despite my feelings towards the 4th move, I have given a great mention towards Focus Punch in the comments, and went as far as to copy and paste what you told me. I'm not really sure what the issue is.