Attack power is supposed to be, at most, with the best possible weapons and training, 450 x (level^2).

Now, here's my suggestion:

The best weapons available at a particular level do 450 damage per level. The best one-handed weapons do 250 damage per level - the best usable as secondary weapons do 200 damage per level. (Wielding two longswords is not feasible.) Weaker weapons are cheaper and easier to obtain, but, obviously, do less damage.

Now, obviously, there needs to be an additional multiplier, equal to the character's level. This multiplier is the weapon skill level.

At the start of their adventuring careers, characters may choose one weapon class to specialise in. Classes are fairly general: Spears would include spears, javelins and pikes, One-Handed Swords would include anything larger than a shortsword, while Daggers would include shortswords and smaller. To specialise in Unarmed Combat, a character must have some sort of natural weapon (such as claws); this is treated as an optimal two-handed weapon (450 x level), and does not give the defensive bonus of unarmed martial arts skills. The reason a character cannot specialise in martial arts is that specialisation allows the character to gain skill levels in a weapon without using it, while the martial arts require constant training and dedication.

Weapon skill levels start at 1, and increase with use of the weapon. If the character is either specialised in a weapon class, or actively using a particular weapon type (these are specific, such as Broadsword), the weapon skill level for that weapon remains the same as the character's level. However, weapon skill level may never rise above the character's experience level.

If, on the other hand, a character picks up a new weapon that they're not trained in, they'll start at level 1, and will most likely need some sort of special training outside normal adventuring before they can use the weapon to full effect.