Garchamp is together with Wobbuffet the two pokes that are non legendary banned pokes or usable in uber tier only.
edit: I am no avid pro player myself either. But there are many tactics that revolve around spikes. Which will hurt any poke that gets switched in and more if it is your weakness and less when not. This rock move as it is makes it very dangerous to switch some pokes in.
Seems like I always used top tier back in the red/blue days. With Snorlax, Exeggutor, Zapdos, Slowbro and Starmie. Now a lot switches of course with most notable Exeggutor getting from top to bottom much like Falcon. Horrilbe moves and the special split killed him for sure. Base special was 125 for both offense and defense. Since Silver/Gold they split it so most rock pokes and some others stand more of a chance. Alas, for the poor Exeggutor it turned into base 65, which is low. Almost twice as low def as before. I love this poke but he is so horrible now
. He still got massive amount of power but he has too many weaknesses.
I talk to much about pokes which is uninteresting for you
.