Yes. I'm not joking.
Here:
Feat[]
“ | At the very dawn of the Imperium, a time of great deeds and mighty battles, Ferrus Manus broke the darkness of the world of Medusa and became the shining light of its people. The sky, perpetually darkened by a great calamity of the long gone ancients, was ripped asunder as Ferrus descended from the heavens amid a great inferno of light. Never before had the primitive human clans of Medusa seen such light, and they were awed and frightened by the fiery display that burned their eyes. The great star crashed into the highest mountain of Medusa, Karaashi, the Ice Pinnacle. The impact shattered the mountain top, burying Ferrus deep in the ice in a tremendous explosion of steam. The land shook under the impact which could be felt the world over. Mountains were toppled, and great chasms were formed as the world rumbled under the coming of the great Primarch. | „ |
~ Index Astartes - Iron Warriors |
Ferrus Manus' pod crashing into the planet of Medusa leveled mountains and shook the entire planet. It endured the crash, and Manus broke free from the pod with his own strength.
A bit vague, but definitely at least Large Island level. Luckily, there's another, more detailed version of the feat.
“ | He was alive, and that stark fact alone surprised him. Cylindrical walls of buckled silver encircled him, a capsule of metal that he had no memory of being placed within. Light streamed through a large tear on one side of the tube, shimmering and inconstant, like sunlight reflected from the surface of a tidal lake. He had never seen a lake, but knew instinctively what one would look like, how the cold waters would feel on his skin and the sense of freedom that would come from swimming the bluegreen depths. |
„ |
~ Angel Exterminatus |
So, a crater which is a least a hundred kilometers wide, and of vaporized / melted rock no less? We can actually calc this.
The Calc[]
Using this calculator and a radius of 50,000 meters we get a volume of 2.61799E+14 m³ for our crater.
Vaporization of rock is 25,700 j/cm^3. The crater has a volume of 2.61799e20 cm³. So that
1cm³ = 25,700 joules
2.61799e20 cm³ = X
X = 6.7282343e24 Joules or 1.60808659178 petatons of TNT
Hope I didn't screw this up. Once again scales to Ferrus since he endured the fall and broke free of his pod. Also to other baby Primarchs since they also broke free of their pods.
So yes, this confirms that Baby Primarchs can indeed solo RWBY, God Brothers included. And the HST is next.