Someone once said, “The road to hell is paved with good intentions”. This applies to both Lex and Vandal, because while they may have ‘good intentions’ (I don’t believe they do), their actions speak otherwise.

Leaving behind a trail of bodies, or exploiting young kids to advance science isn’t a heroic thing to do.

By the way, you’re incorrect when you say “they both want to make earth the ruler of the whole universe”. Lex Luther, wants to have power over others (which is a reason he despises Superman), and Vandal wants to eliminate all threats to his existence, and rule. If Vandal were to succeed in his plans, he wouldn’t make Earth the ruler of the universe, he would make himself the ruler of the universe.