Nope, my first playthrough was on easy. My melee party member always died if he was alone. Well, Aveline always survive because I built her as a tank. When I played through again on Normal, every party member died except me in a lot of fights. What I found odd was they always survived boss fights but they always got owned by regular enemies.
Because regular enemies come in swarms so you apparently handle swarms badly. You need to (well you don't
need to, but if you want to play better and be able to survive on greater difficulties) learn how to control your party against swarms.
Basically it comes down to concentrating the entire party on one enemy at a time. Taking out any mages first is a must, then sneakers (those who cloak and then do backstabs, a smart move if you've got both those and mages attacking you is to stun them while you take care of the mages), after that you either go by weakest-enemy-first or, if some other enemy proves to be too much of a threat to be left attacking for a while, take care of that first. Fully developed area effect spells help a great deal as well, especially http://dragonage.wikia.com/wiki/Tempest_%28Dragon_Age_II%29 which has a chance to stun. http://dragonage.wikia.com/wiki/Firestorm doesn't stun but can help easily take care of a bunch of low-level enemies. http://dragonage.wikia.com/wiki/Chain_Lightning_%28Dragon_Age_II%29, although not technically an area effect spell, is absolutely lovely against a bunch of melee enemies which have gathered around you and are cramped together (or a bunch of archers which are cramped together).