I would like to suggest keeping the orange level 80 bottle drop rates from the Hero of Royal Army Event. The drops are too abysmally low normally, and this event makes the bottles drop at a reasonable rate. The event will be below:

It's time to bring your A game to the Royal Army Raid and prove you can tear the enemy apart just as well as the best equipped player out there! For the next month, we're boosting the stat floor for Royal Army Raids, powering everyone whose gear isn't quite there yet up to 28,000 ATT/M.ATT and 15,000 DEF!

Event Name Hero of Royal Army Event
Event Start Wednesday, December 6th (End of Maintenance)
Event End Thursday, January 11th, 2018 (Start of Maintenance)
Event Details
Stats for all characters in Royal Army Raids adjusted up to 28,000 ATT/M.ATT and 15,000 DEF, if below those amounts
Improved drop rate for Mysterious Glass Bottle (Lv. 80)