A good sword to a not so good sword has a lot to do with metallurgy and the skill of the smith NOT to screw it up.A good sword holds an edge and is tough enough to handle impacts and cutting. If a sword wards, twists or bends in the hand of a novice then it 's likely not a good sword. An skilled swordman can "use " a good sword to cut because his technique is trained to cut properly. even a bad sword CAN cut.
A reputable smith can forge a strond blade with no micro cracks in the steel. these micro crack and stress fractors can eventually lead to the demish of the blade during use.
Metallurgy -wise the steel has to be harden enough to hold a good edge but tough enough to withstand impact.
Good swords flex