Ok, modding a game is not even close to making balance changes to a game that has been global for nearly 2 years. That's a whole other explanation
The examples you're giving are much more specific. The wrong Omega-x in a rotation? Clearly they used the wrong call. As soon as it's brought up, any programmer working with that code should instantly know the fix - swap out the incorrect call for the correct LR dm Omega-X, save/deploy, just needs to be updated client-side. New mon was just released and skill is too slow for that rarity? Again, quick fix for that mon.
Reworking a bunch of old mons is a completely different task. You have to consider the entire game and how those new stats/skills will affect the current player base, which is comprised of veteran and novice players. That's not the same as releasing a new event with a new mon, seeing that its skill is 1 turn slower than previously released mons of same rarity/skill, and decreasing the cooldown by 1. Those are different scenarios.
Reworking a large amount of skills and stats requires looking at the bigger picture, determining who and what needs to be changed, considering how it affects the game and other mons of the same rarity, lower rarities, higher rarities, free mons and cash mons, as well as what they have planned to be released in the future. And on top of all of that, you have to keep in mind time and money restraints. You can't just let your game sit while nothing is done, ESPECIALLY with a mobile game. People will move on. This isn't a triple-A console title that someone paid $60 for and has hours and hours of content built in from the start, this is a mobile game, meant to be played in small bursts, that requires weekly/bi-weekly events to be swapped out in order for new content to come in, preventing new and old players from quickly becoming bored with the game and abandoning it for the latest trend in the app store.