The Bipedal Heavy Combat Unit, and of course, the Giant Araneae Combat Unit

On this alien world, lived a species of omnivorous bipedal giants that was just shorter than the Arc de Triomphe from Paris. Another known species of giants was an arthropod that was the size of a giraffe. Whilst they did not have human intelligence, not yet at least, they were entering the Stone Age, very slowly.
One day a blue portal opened in deep space and a ‘satellite’ of sorts came out of it. It studied the planet, if it’s hospitable, if it’s environment is right for.. well, you shall see. About four days, two portals opened, one brought more satellites that moved to different sides of the planet and the other was sub-orbital, a pod appeared from that portal and landed. Humanoids, that seem to only have the vertebral column and ribs for a torso, holding firearms came out of it, along was a drone on top of which was some ‘mollusc’. They went and captured the first organism they found, it was one of those giant arthropods, they studied it; then sent the information back to Overworld.
A month later orbital and sub-orbital portals opened, far too many of those ‘soldiers’ came out, maybe millions? Numbers don’t matter.. they conquered this world in less than an hour and captured every living organism, then studied these organisms just like before.
Whilst there were many species, only 2 were important, one which is used to conquer primitive worlds, and the other helped in conquering Earth.
What happened to those 2 giants? My answer is going to be quite straightforward, let me describe a scene.
A giant bipedal alien with its hands replaced by a rotary cannon, shooting bombs, and the other one has a cannon that shoots a ‘plasma beam’, its face was replaced with a camera; it is marching forward with those ‘soldiers’ that are on the ground. Besides these 2, on the ground and on this giant’s shoulders, are also those arthropods without abdomens, shooting rockets at targets. I do not think this medieval world will even last a day..

I hope you enjoyed, this is just the backstory for 2 of this empire’s Combat Units, not the whole story of the empire.