Keep in mind that you probably watched an international game given that it was on TV in the USA. Yes, those players are insanely large and powerful but if you saw a pro defensive tackle walking down the road would you think you couldn’t play football? The beauty of rugby is that there is a position specifically suited for every shape and size.
The beefy players make up the highly skilled front row in the scrum while the taller players are the jumpers in the line outs. Slender zippy players zig and zag and are extremely deft at running the ball in the back line. Short – tall – bulky – slender – fast – slow there is always a place for you on a rugby team and you will definitely get your chance to run with the ball or tackle someone else running with it.