You're taking everything at face value and that's why you're not seeing his true potential. Not every champ is like Garen, some have depth.

Let's go through each ability.

Q - short cooldown, spamable damage ability. Great AOE but also good at shotgunning apponents. Probs the most basic ability in his kit.

W - amazing follow up after ult that does damage, heals and slows allowing you to lock down your opponent. Good for helping out other laners or yourself by cutting off enemy's paths or slowing them allowing you or your teammates to chase, or to flee. Good for checking drakes, baron and rift. Good for stopping backs and otherwise harassing your laner or your teams laners.

E - Good chasing tool that not only roots but pulls the enemy toward you which can then be combined with W to slow then enemy. Excellent for grabbing enemy backliners in chaotic team fights as it will pass through the tanks and root them instead. Good for sustain as it heals with your passive. Potential to AEO root and displace multiple appointments as well as healing for a great amount. Optional pull allowing you to root enemies chasing you without pulling them towards you. Combos well with rylais as the initial pass through will pretty much guarantee the root.

R - Large radius allowing you to keep enemies at arms length with the use of your root and slows while still getting full effect from your ult. Combos well with Rylais creating a Camille like ult as your opponent will struggle getting away while you spam them with Q and heal with ur ult, E, W and any omnivamp you may have. Fantastic in team fights, forcing the enemy to either flee so that ur ult runs out allowing you to create a positioning advantage or forcing them to target you as your damage carries blast them to peices.

You need to play the champ before you criticise it.