Did you think Light was the hero when you watched it the first time? He's a teenage kid who suddenly gets way too much power, thoroughly abuses it, then starts killing innocents to avoid the consequences of his own actions. Even if his first few kills were literal supervillains, there is no justice in a world where Light decides who lives or dies.

Your idea of a revolutionary undermining the system is also an interesting story idea, but it's a very different story idea.

That's kinda the point, Light is an ergonomical lunatic with a god complex who very early on starts killing more or less innocent people for the insult of getting in his way. He isn't an anti-hero he is a sociopathic lunatic who if he was in a grimdark setting would be sitting next to Griffith and FUCKING Erebus. Hell he isn't even all that complex since at least say Erin Yeager had the excuse of getting mind fucked and being put into a bad situation by himself, his ancestor, and the fact the world was genocidal to his people.

Well, he thinks criminals are such because they're evil or something. He thinks the only way to stop them is by creating a totalitarian state where he is God and everyone does his bidding lest they invoke his ire.

The thin veil of "making the world a better place" was lifted super early in the series, when he started killing people that weren't criminals, justifying it as "if they go against my plans they may as well be criminals".

He was never supposed to be a good guy. He's an arrogant piece of shit, and that's why he got caught.