But say that Tyranitar was a Boah anyways, so you couldn't really have walled it due to Ice Beam. You want to be able to counter the most you can while also staying in the "general" realm where you don't have a specific counter for everything. That's why Pogeys like Blissey, Gliscor, and Cresselia are so popular. They can counter almost everything in their defensive spectrum.
The team plays a large part in showing your skill level, but even if you have a great team you can still suck. Prediction doesn't define a player's skill as much as people think it does - common sense and the ability to think of the best and worst possibilities and moves that you can make are what allow you to get a good base in battling. After that, keeping on top of the metagame, constantly trying out new things such as a different EV spread or moveset, and battling a lot is what makes you better. As my track coach says, if you're not continually practicing, you can only get worse.