the secret is you hit guys with the axe until they die. 

Oak is possibly the worst character in the early game... however... once he starts leveling up he becomes very, very powerful. Oak doesn't excel at anything in particular, which lies is greatest strength, he is an all-arounder. He can dish out more DPS than most characters, can stun/slow with pentitence, can summon minions, has one of the highest auto attacks in the game (with souls), has a shield that also heals at higher elvels AND let's you use HOL at the same time, decent speed (just as fast as Reg), Last Stand can be very handy, and then to top it all off he has a very good AOE attack. There's a few other things I am omitting, but I absolutely love Oak. You need to practice with him and get better, that is all I can say. He's amazing once you figure him out and use him strategically.

1. Soul Ward I

2. Divine Justice I

3. Penitence I

Buy monks in the beginning and maybe a mana pot.  I've been using the Blood of the Fallen lately because the extra hp and health regen is huge in the beginning and lets me focus more on damage later in the game.

Did our match a minute ago just show you what Oak is good for?

Oak is a tough cookie to get used to playing. I had the advantage of playing him a lot early on when everyone was just learning the game. You're probably going to have a tougher time with it when playing against experienced players.

Oak is an excellent general

Oak is an excellent assasin

Oak is excellent as a gen/assassin hybrid

The trick is knowing how to pace yourself in early encounters. Don't expect to wrack up a ton of kills pre-level 5. As in that movie above, learn to love the term Tactical retreat.

Speed (swift ankelts + boots of speed at level 1) is a great way to start for a more assassin oriented build

Mana helm + teleport scroll + heal potion is another good starting combo for a more general or hybrid oriented build (plus swift anklets favor item)

Learn how your skills compliment one another. Every skill Oak has is useful on its own, but when you combine them effectively they make for deadly combos.

Here are a couple of examples - 

Using penitence to open a fight, get close to the DG (away from towers) and pop surge of faith. Follow with another penitence and start chasing the enemy down. your penitence slows + debuffs, while your surge of faith increases your attack speed. As he retreats (and he will) chase until just before you hit the towers. If you almost have him down, hit shield just before you get in tower range, finish him off and make a speedy retreat.

If you decide to take raise dead early on, make sure you put at least one rank into soul power and focus on always having at least 2 ward flags up. This ensures your attack power is maximized by the added spirits (I think its +40 weapon power, +20 for every 3 spirits you have up). Combine this with penitence and lure the enemy away from their defenses. If you mock like running away, while at the same time sending your spirits to attack the enemy DG, they will generally follow you. As you pull him far enough away, hit with penitence to slow him down, turn around and start wacking.. The slow movement speed + your spirits chopping away will often catch and enemy DG by suprise and you can finish him off before he can retreat to his towers. 

The nice thing about Oaks skill trees is that you can create amazing hybrids that pretty much allow you to max out your most important skills while still being able to round your character out with the rest of the skills in the tree.

In games that I hit 20 I usually have something that looks like this:

Penitence maxed
Surge of Faith Maxed
Spirits to level 4
Shield to level 4
Divine justice to level 4
Soul power at level 1

The only skills I don't often take are Last Stand (or whatever that one where you turn invuln after you die) and morale, although I sometimes take morale if I've got all my level 4 idols and a high rank of Raise Dead before level 10. Maxing out your Morale will help a lot in the late game if you're a minion oriented player. Otherwise they tend to get one shotted by enemy AOE's. 

There is an easy way to curb how much he sucks.

Take whatever skill you want at level 1. Take Blood of the Fallen. Buy Monks, cast and sell back. Buy Banded Armor and Scale Mail. You'll have 1000 Armor and 2900 hp at level 1 and be literally unkillable without HEAVY 2v1 situation or dry-humping towers.

Oak is a powerhouse, lvls 7+, early game buy priests, summon, sell them (if careful priests will last long enough for you to get HoL), buy armor and a mana pot.  Go to first flag, position priests behind you between yourself and a your towers out of harm's way.  You'll have a HP pool to outlast anyone with blood favour item, if it's a melee battle, pull up your priests to start healing you, if you're getting spat on/ranged down pull back to your towers, your priests will heal you as you retreat since they're already in position. 5+ you start getting mad XP with that aoe skill of yours.  

End game I remember I was doing 450+ damage per swing with .7 attack speed, and that's with a few armor pieces thrown in.

Having someone who sucks at the game make wild assumptions based on how bad he is with a certain character doesn't show balance in any way.

I think Oak is kinda faceroll if you know how to build him. He gets so many minions so easily, and +M stats have such a large effect on his damage because of that. I just played a game where I killed an early oak 5 times, and he came back to rofl-stomp the match. Oak is the only hero i know that can do that so naturally.

Spirits get kills, is the general message. Especially after pent and buffs. He and erebus have quickly become 2 of my favorite heros.

I wasn't talking about you directly. But if you want, I can.

Isn't The Oak the Demigod that Frogboy prefers?

If he's going for a minion-heavy build then parasite egg will work wonders. Every time you hit the general his minions will take the damage as well. A couple of strong hits should be enough to kill his entire army.

And like the others said, he's weak early game. Harass him continously and don't let him gain experience.

Doesn't make him underpowered - I'm certainly not recommending a buff.  Just makes him a less attractive Demigod than another.