Keep in mind that the Weaponsmith is a support character, not a primary fighter. If the Skyraider and Swordmaster are challenged in combat, and the Weaponsmith can't hit anything, that's fine. It's not the Weaponsmith's job to hit anything. His strength lies elsewhere.
In general, though, Earthdawn doesn't need a carefully tuned balance. Challenge the party as a whole; everybody has different talents that contribute to the final success (or failure). It's true that some classes take a while to really get into their own. But more importantly: fights don't have to be predictable. My group has lost fights we should have won, and won fights we should have lost. When things go wrong, you can still improve your odds by spending karma, and when that's not enough, well, you need to think on your feet, which is where the real fun is. Sometimes you need to run or strike a deal. Sometimes you get captured and need to escape, sometimes one player has to rescue the others. Sometimes failure can lead to interesting things.
And in Earthdawn, even much weaker characters can still contribute their unique abilities. My group also had a PC die when the group was around circle 4 or 5. The player started a new character, a Swordmaster, at circle 1, and managed to contribute fine during combat. One thing he did was to focus on one specific talent (Maneuver) and maximize that way ahead of anything else. He could make himself hard to hit, and that way he could keep one enemy busy while the rest of the group (a Warrior, a Skyraider, a Nethermancer and an Archer) tore through the rest of the opposition. He punched way above his weight, but you need to know what the strengths of your discipline are.
And once the players have figured out how their disciplines work and how they interact with each other, you may even throw "impossible" encounters at them to see them get creative. Nothing is cooler in GMing than seeing your players do the impossible. Just don't expect it of them every single time. And give them and yourself the time to figure out what they're capable of. Start out easy, and keep varying and increasing the challenges until you reach something that works, and then you continue varying, as every combat (and every non-combat encounter) needs to be unique. And if it gets too hard, give them some space to recover.
