Well the main problem is we don't know the damage algorithm you use.
My suggestion is to get familiar with the numbers produced by playing with them when working in an RPG Maker series game. This is also important when using battle systems that change more than the view.
Even then the question really depends on the game.
However there are formulas you can use to make games more high, low, or balanced end.
If we use % more, we now have a more high end focused game, where spells and skills from earlier are still relevant late game. You see this in use more in western games.
If we use more flat numbers, we see more low end power, where skills lose their relevance as the game progresses.
We get more balanced power by combining these and/or using them in relation to stats that grow on party members. For example if you tie a skill to more agility factors, then the skill stays useful for more of the game, especially to agility focused party members.
You also see more exponential growth with x*x factors over x+x factors. In the scenarios of x*x the character will grow a lot stronger every level, exponentially. Where level 1 to 2 is not huge, but level 66 to 67 gives huge bonuses.
When working with defense it's also important to note a % reduction, which means early game enemies will still be relevant late game, and a flat reduction where early game enemies don't scratch you.
In order to balance weapons you have to understand this. Remember, if you have to use decimals just upgrade by 10s to save yourself trouble. You're better off working with integers when it comes to displaying information to a player. When determining weapon growth, decide what % better you want the player to grow when equipping a new weapon.
So if he hits for 80 and you want him to equip this new weapon and hit 25% harder at the same level, take into what factors you can (Like average level when getting access to this weapon) and try to make him hit for 100 at this mark. The same can apply to spells.
Personally a % growth is the easiest way to do it.