Jonnie's problems start the chapter he's introduced in. From the moment we meet Jonnie, we're given no reason to like him: he's sullen and angry, bullies a family member with cold stares, and ignores his girlfriend on his way to browbeat the village into doing what he wants. Now granted, this is right after his father's death and lack of a funeral, so you can excuse Jonnie's behavior due to stress (even though it doesn't change much afterward). But it's still a terrible first impression. We could have been shown him before his father's death to get a better look at what a normal, happy Jonnie is like, so the sulkiness would be meaningful and we could tell when he's recovered from it. Instead we meet a jerk, and then he becomes a stoic adventurer, and then he's an angry captive, and then he's an angrier resistance leader.
In the moments Jonnie isn't being angry or a bully, he's... well, hard to describe. Despite being the book's main character, there isn't a whole lot to Jonnie. Sure, he does plenty of stuff and has a staggering list of abilities and accomplishments - ace pilot, dedicated outdoorsman, unbeatable warrior, and so forth - but he has little in the way of personality. He's not a charming rogue, a wide-eyed idealist, a taciturn intellectual, or anything like that. He just spends the book doing things, going places, and killing.
We can infer some things about Jonnie from his actions, at least. He obviously hates Psychlos, and doesn't like any aliens meddling in human affairs. He finds those Brigantes disgusting and contemplates strafing their village without any exceptions for women or children. Jonnie has trouble with the idea of noncombatants in general, and doesn't lose any sleep over the uncounted Psychlo women or children he killed. Nor does he see anything wrong with joking about killing prisoners to let off some steam - or rather he is incensed when Psychlos torture a captive to death, but will laugh at the thought of doing the same to his Psychlo prisoners of war.
On the more positive side, I guess Jonnie cares for his fellow villagers, given his attempts to make them move to a less irradiated area. And every now and then he remembers to worry about his love interest. And he's humble enough to shy away from the fame he earns over the book. And he's nice to his horse. But that's all just the bare minimum of motivation, since otherwise Jonnie would be acting at random. Beyond that, there's not much of anything. Still more than Chrissie, at least, but Chirk is probably better-developed than Chrissie.
That's another thing - character development. Jonnie doesn't change. He's the same bland hero from the book's beginning to the end. Sure, he learns a lot about the universe and how to fly a spaceship, but there's no arc of Jonnie coming to terms with the burden of leadership, no meaningful struggle with the needs of humanity as a whole versus his desire to go home to his village, no culture shock from learning about alien civilizations. Jonnie travels all over the world, but has no comparative mental journey. He is a man who can blow up a planet and emerge unchanged.
But all of this does nothing to hurt Jonnie's popularity (at least in-story). Strangers are willing to follow him before they even learn his name, and there was that nauseating moment when he was elevated to demigod status by some tribes. You can tell who the bad guys are because they're the only people who dislike Jonnie or dare to go against him. To Hubbard, Jonnie is the embodiment of all that is right in the universe - and if this statement disturbs you, good, you're paying attention.
Now there's a concept I've thrown around before, that of the "Mary Sue" or her male counterpart "Marty/Gary Stu," which I should probably explain further. The term comes from fanfiction and is used to describe obnoxiously perfect characters, the ones who warp canon around them, tend to be princesses and/or half-elves, make the entire cast fall in love with them, and bear a striking resemblance to the idealized version of the 14-year-old girl writing the story. While Jonnie lacks paragraph-long descriptions of his lavish wardrobe or exotic eyes that change color with his mood, he does share some of the Common Mary Sue Traits:
- No personality
- Able to convince an entire Scottish village to do his bidding before they even ask him his name
- Perfect physical condition, able to beat a bear to death without injury, even though his home village is blighted by radiation sickness and mutation
- Elevated into pantheons by cultures who have never met him, attains a messianic status in multiple alien civilizations
- Prince of Scotland (by blood transfusion)
- Becomes wealthier than God
- Blows up an entire species, but nobody blames him for it or considers it a bad thing, even the last survivors of said species
- Allegedly, his portrayal on the cover of early editions of Battlefield Earth bore an uncanny resemblance to L. Ron Hubbard.
And that's another thing - Jonnie has no flaws. Or rather, no flaws that are presented as such, save for those not-really-flaws like "he doesn't know when to quit" or "even if it's impossible he'll keep trying until he beats it." His decisions are always right, and his failures are due to sabotage or insurmountable obstacles rather than his personal failings. He's so good at everything he does that there's no drama when he gets in a fight or is presented with a challenge, just a wait until he achieves his inevitable victory.
Consider Luke Skywalker. When we first meet him, he's a whiny farmboy, but we can sympathize with him wanting to get out and see the world and make something of himself. He makes mistakes and rash decisions that almost get him and others killed, but he learns from them. The new powers he discovers are almost secondary to his personal growth. And I'll also point out that even though he learns that his sister is a princess, neither George Lucas or any expanded universe writer I've encountered has dwelt on the fact that Luke is technically a prince.
Consider Harry Potter. He starts out embodying a child's wish fulfillment, the understandable desire to be told that your mundane, unpleasant existence is illusory and that you're really someone supernatural, special. But his story is really about growing up, about facing your fears and taking on responsibility, even if you don't think you're ready for it. Harry makes mistakes - terrible mistakes that get his loved ones killed - but matures enough to surpass them and succeed, with a little help from his friends.
Jonnie starts out physically perfect and angry, and I guess we're supposed to empathize with him like we would a rebellious teenager, though really he's right (of course) and his fellow villagers are idiots. His story isn't about growing or changing because Jonnie's pretty much perfect already, though he does get taught how to fly a plane and do math by magical science. He has some struggles and setbacks, but they're always due to outside forces beyond his control, and he eventually outsmarts them or blows them up anyway. And he's heaped with praise and titles and treasure in case none of the explosions leave us suitably awed.
That's Battlefield Earth in a nutshell, really: some guy going around blowing up aliens and bullying the universe until it better suits him, and we get to watch.