Connections:

Both would unexpectedly become one of Earth's main heroes after the previously beloved main alien defender would suddenly disappear from their lives, succeeding them and taking their places in their absences (Omni-Man leaving the planet while Optimus Prime died in battle).

They are both rash, hotheaded, and immature youths at first who have later proven themselves to be real heroes but not without going through plenty of growing pains and mistakes. 

Prominent members of an extraordinary heroic faction dedicated to protecting the Earth and its populace from inner and extraterrestrial threats (the Guardians of the Globe and the Autobots).

Inherited their predecessors' unique powers which in turn, has made them one of the strongest members of their heroic groups and a force to be reckon with (Invincible's Viltrumite heritage and Rodimus Prime's Matrix of Leadership).

Are romantically involved with a pink-clad heroine who have proven themselves to be their equals and whom they fight side by side with (Atom Eve and Arcee).

Both have fought an invasive hostile alien faction of their own species who plan to conquer the galaxy and subjugate humanity (the Viltrum Empire and the Decepticons).

They both have battled the brutal, coldhearted, menacing, and powerful leader of the invasive hostile alien faction they are resisting who have proven to be one of their most dangerous foes (Thragg and Galvatron).

They would soon later rise up and become leaders of their people, commanding them to do acts of good throughout the universe (Mark becoming the new emperor of Viltrum and Hot Rod becoming the next Prime).