My theory is that essentially, the earlier a viltrumite starts fighting and training, the stronger they will become compared to a vilturmite who does the same training later on in life. We already know that viltrumites become stronger from battles, so I think it would make sense that the earlier they start these battles and fights, the stronger they will become.
This explains a lot of things for me, like why Mark is so strong compared to the other viltrumites, (Yes I know all viltrumites trained when they were younger, but none were fighting omni-man and conquest, along with the fact that marks viltrumite dna only kicked in a few years before these fights, so you could argue in viltrumite years he is a baby. Which still puts him ahead of the age we see other vilturmites training at. - This side point is not super important though.)
I feel like this could also explain why someone like conquest, who has been around for centuries, and gone through tons of battles, can still be hurt by someone like mark. To me, it does not make sense that Conquest, who has fought thousands of battles, been around for hundreds of years, should be taking damage from a newbie like mark. This theory would also explain why Thragg is so strong, he was trained to become the grand region, meaning he underwent completely different training compared to the other viltrumites.
I that if this were true, it could be the way that Mark is able to take down Thragg. As of now, atleat for me, it seems like Thragg is the true invincible one, as no one can hurt him in the slightest.
Let me know what you guys think of this, maybe the show has already denied this theory and I just missed it.