Normally, killing magical beasts should yield no experience.
It's much like hunting small animals.
Although magical beasts possess strength comparable to Transcendents, they actually do not have a clear Transcendence level. Their level in the game simply indicates "the extent to which their strength is equivalent to that of a certain Transcendent."
Although Aiwass's memory of the "experience" setting was somewhat vague, he roughly knew that "free experience" was indeed related to the natural dispersal of Path forces during intense battles when killing or expelling opponents. Because the forces of the Path naturally flow from higher to lower places, and the system merely serves to open up a channel for reception.
But basically, only by killing a Transcendent who is stronger, or at least on par with oneself, can one obtain experience.
Therefore, this is essentially a "Transcendence" ritual.