There are a lot of factors to consider when evaluating your weapon's performance in battle. To this end, we have compiled a short list below that includes most components that might affect the outcome of a PvP arena match:
1) Weapon upgrades play a big part on a player's damage output. A low tier weapon can increase its power drastically if its fully upgraded. The higher a weapon's tier, the more a player can upgrade it, thus increasing its power.
2) Customizations (patterns/decals) can increase a player's defensive or offensive power in battle. You can check if a player is wearing any form of customizations during a match by bringing up the leaderboard, and checking the customizations column.
3) Gear can increase a player's defensive capabilities, by raising their gear score. The higher the gear score, the less damage that player will take. You can check a player's gear score during a match by bringing up the leaderboard, and checking the gear score column.
4) Headshots always deal double damage. If you are comparing your damage output to another player with a similar weapon score, make sure to factor this in to your comparison.