[Paracelsus]

all the servants rely on their masters to provide them with magic powers to keep themselves functioning. The contract comes with a link between the servant and master, and magic power is automatically provided to the servant through that link.

*cought*PACTIO*cough* <_<

But class is still very important, no matter how lousy the master is, a Saber class will (most likely) not lose to an Archer class in a melee battle.

Spoiler:

so lancer has just been lucky to find the "weak" saber, otherwise she would have owned him in no time <_<...as regards Archer he still is a peerless "sniper" so he could hit saber avoiding a direct clash.