I've been playing private servers for 20 years and I've seen many succeed and fail. The trick is to find a balance. There are lots of little changes you can implement to make this server seem more player-friendly.
Make higher-tiered gear drop more frequently
Make the penya drops higher
Increase the upgrade rate
Increase ways to obtain soul-bound diamonds
Make Gatcha a 1/4 of the price
Make the chance of getting gear, and higher-tiered pets in Gatcha higher
Allow more attempts at dungeons and challenges
Create a penya shop for cheap often used items
That's just to name a few. The ways to make this server different from retail are endless. Is it a trade-off, are you giving away profits? No. I've spent hundreds of dollars on private servers that gave most things away for free. These servers always have a healthy player base and they were super smart about finding things spenders will pay for.
I'm a moderate spender and I like your server. I've spent 15 USDs so far. I'm hesitant to spend more because it feels as if your basic plan is to increase the exp rate a little, lower the price of diamonds and give coupons on Facebook. That's just not nearly enough to make a private server succeed because people will log on, play for a few hours and leave. Not even big spenders want to play on an empty server.
Please take my suggestions in the spirit they were intended.