When someone loads up bio, you basically can't act aggressively towards them, movement-wise. The only thing that works good against bio is hitscan.
Bio doesn't take a lot of skill to use, like so many pub players think. It takes a whole lot less prediction than rockets to use effectively. The only drawback is the rof. Bad players don't like the rof, but that's the reason why the number one use of it is over or around corners while running backwards, or making easy annoying pickup shots. The biorifle doesn't take an incredible amount of skill to use, compared to hitscan. You don't need a lot of mouse dexterity or movement skills to use the bio effectively, you just have to realize it's applications, weaknesses and strengths and play with it accordingly.
It's by no means a weapon players can outlet a lot of skill into effectively, because it's applications are so limited, and the only hardcore, non-defensive frags are because of ping, packetloss, lack of awareness, or plain stupidity on the recieving side.