At each stage of evolution, new obstacles appeared before the Phantom. The Phantoms were not unique in this; monsters also had to pass through many barriers to reach their true power, but the Phantom way was always much more difficult because the conditions were specific, and they could not simply absorb a lot of energy and begin evolution through force.
This becomes especially evident when the Phantom reaches the K2 Level and is faced with the task of destroying the Two Walls, then at the K3 Level, the Crystal Gates appear. Sure, the K0 and K1 Levels also had their challenges, but with each level, they became more difficult and longer.
No one was surprised by this; every Phantom was ready for new, more difficult trials to climb higher on the evolutionary ladder.
But... the K4 Level was different from all the previous ones.
If the Second Rank Phantoms and Lords did not exist, this would have been the peak of evolution, and to some extent, that was exactly the case.