Physical unfairness to GB swimmers

I don't follow swimming much apart from when the Commonwealth or the Olympics are on. Anyway, I have found that it really Isn't fair that someone as small as Fran Halsall has to compete against other swimmers who are physically much bigger and stronger than herself. The same situation also applies in the men's swimming events where guys like Phelps, and especially Ryan Lochte are massive and huge with big wide shoulders and chests when compared to many of our own swimmers like Tancock, Renwick, Carry etc.

They have weight classes in fighting, lifting, rowing and eating events ...why not shooting?
Cycling for fat blocks?