mana

Garens one of the few people who beat darius in lane though...

Garen is fine IMO. He is 100x tankier than Darius, has safer laning due to his manaless nature and actually having an escape/sustain. He doesnt do as much damage as a trade off for being able to take more damage, having some mobility and being manaless. We call that "game balance".

I play Garen as a roamer. Push out my lane with spin2win and then sprint to mid or go for the enemy jungler and put pressure everywhere.

Darius ulti also does more to targets that stack armor, since it's true damage based on the stacks of his passive. Targets that get a lot of hp (read cho'gath/singed) are better suited for Garen since his ulti scales off missing hp points. Building brutalizer on Garen is hilarious because no mana (also black cleaver rework in S3 but that's not for a while). Brutalizer also builds into youmuu's so that I can get to who I need to very quickly and keep them out of a fight. CDR, flat armor pen, and crit too, all very nice things for Garen.

On Garen, I tend to build boots 3x pots->HoG->boots of choice->avarice blade->sunfire cape for extra everything that Garen is a fan of->youmuu's/randuins. Youmuu's if I'm having trouble keeping up with people or getting into fights, otherwise I go for warmog's->finish youmuu's. Tends to work nicely but games never last that long anyways lol.

But hey, don't listen to me. I probably don't know what I'm talking about at all, I don't actually play this game a lot.

Spin to win does 741.15 base damage + 330% scaling at max level (for people looking it up, remember it scales on total AD, not just bonus, so include that). That's basically Darius' entire kit, and before counting Garen's Q. Garen has a movespeed button that cleanses slows and can also silence. Garen gets a ****ton of free defensive stats in addition to a % damage reduction barrier. Garen is a resourceless champion, though Darius isn't super restricted by mana so this isn't huge.

Garen's damage is less useful for quick trades, as he needs to stick to a target for full spin. He can also spin less frequently than Darius can. Garen's ult is in most cases inferior due to magic scaling and obviously not refreshing.

Garen has a solid health regen passive for laning, Darius just has more damage for trading. They both have perks and problems. Garen is overall more defensive, Darius is overall more offensive. Garen will usually win a lane between the two.

because just because they both have a single target execute that means they need to be in complete balance with each other?

well i guess next we should make elise's skill shot stun thing scale with range like nids spears.