My suggestions:
1. Test all new stuff BEFORE you release it. Gear, pets, maps, what have you. Check, double check, triple check all the most important details - for example in this case: weapon damage, weapon skill damage, proc usefulness, proc rate etc. Compare those details with other gear/pets/whatever - in this case with the recently released myth weapons. Test new stuff in actual game environment - do some runs, check the times, pay attention to how the proc works and how often it occurs, play some pvp and so on and so forth.
2. Do long-term planning. Examples follow. When substituting a system in this game with another system, plan accordingly in order to make sure the new system is an upgrade and not a downgrade (e.g. jewels vs gems). When releasing a new weapon, plan ahead - have at least some idea when the next few weapon releases will be, what the next few weapon releases will be, how they will compare to your most recent and/or most powerful weapon etc. etc. Make sure you don't release both complete disappointments (e.g. glintstone set) and totally overpowered stuff that will be hard to replace in the future (e.g. arcane ring). Release stuff periodically and in the right times (e.g. don't release arcane weapons a couple months after same level/same type mythic weapons and a couple months before a 10-level-jump new cap).
I can add many other things, but I'm pretty sure it's not worth bothering. Those two I deem important enough to share though.
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