Man, talking about 'Invincible' always gets me hyped! Mark Grayson's journey from a rookie superhero to someone who can hold his own against Viltrumites is insane. But strongest? Nah, not yet. Nolan/Omni-Man was wiping the floor with him early on, and even later, Battle Beast and Thragg are on another level. Mark's strength is his growth—he's scrappy, learns fast, and has that human/Viltrumite hybrid grit. But raw power? The series shows him getting wrecked plenty to remind us he's still climbing. That's what makes his arc so satisfying—it feels earned, not handed to him.
And let's not forget the Viltrumite empire itself. Those guys are built different. Mark's got potential, especially with the timeskip upgrades, but calling him the strongest undersells how terrifying the top-tier foes are. The comic doesn't shy away from showing him outclassed, and that's why his victories hit harder. He's not invincible in the literal sense; he's invincible in spirit, which is way more interesting.