I don't necessarily believe your story, specifically.
While yes, the buff changes will make leveling less explosive from the get go, it takes 5 minutes to level to 6, without buffs. Anyone who quits 5 minutes in is probably not a reasonable person to use as an example.
Having said that, there are legitimate complaints about leveling. Grinding as a gameplay concept is outdated. There is no need for it, and in today's market with MOBA and Digital card games [I mean, REALLY??] utterly destroying MMORPG's in player numbers, revenue, and ultimately success, it is high time the leveling and progression got an honest and fair amount of attention. And I'll give 3 reasons why, SOLID reasons.
1: The largest portion of ROSE is veterans and loyals, meaning they're all at end game content. This makes for empty and desolate zones, if a new player feels alone for the entire time AND they're not having fun, they will just give up after a few hours.
2: When you need to augment the leveling system with Medals, Events, Costumes, Party Systems, and more just to encourage Veterans to make new character, then you have a bad leveling system. Even veterans here today don't want to level, atleast those who don't just bot their way to it in 3-4 days.
3: Todays market games are no longer a test of patience and will. They're moving towards fun, jump-in and go style games. There is nothing, I repeat, NOTHING for them to do BUT grind. Want to do Dungeons? Too Bad. Want to do some public events? Those don't exist. Want to play some minigames or work on a profession? Nope, can't do that either. Literally, the only thing they CAN do, is grind. Pressing those 1-2-3-4 for 154 hours until they finally hit 200, and get a taste of dungeons. No one in their right mind would ever play 154 hours, just to see if they like the only supported content in the game.
Now, aside from those 3, I also listed market proof of trends and changes the gaming economy and consumers have gone through over the last, 11 years? If ROSE wants to stay relevant, and more importantly running; then a change is a must. If it takes ramping the exp up by 10x, so be it. But a change is needed. Not some complex additional system to augment a horrible base. Just fix the base, or multiply it. After that, you can focus on the extras or making more content for end-game.