It may not be adept at speed on land, but that's only relative to experts in the Blood Exchange Realm; in fact, its speed is far faster than those in the Five Organ and Viscera Realm. The reason it couldn't catch up to Murong Yan earlier is that it's even less skilled at Soaring Flight Escape. On the ground, however, Murong Yan would hardly be faster than it—the speed of this creature could at least match that of some Grandmasters.
"..."
As the Mystic Tortoise made its escape, one face finally sank into complete gloom.
Not having chosen to mobilize the Military Formation to trap the Mystic Tortoise earlier, there was no chance of catching it now unless several Grandmasters broke away from the formation to pursue it alone.