Yea, its a system called resource opposition and its intended, you will never use willpower as a warrior class, you need to find a way how to live with it. Thats one of the key features of the game.
You have BTW a LOT of tools how to manage that, just search items and passives, its all there.

It is working as intended. Part of the gameplay is managing your rage v. Willpower. Rage is not infinite and you have to work to improve your items and use the appropriate passive skills (like "Furious Appetite" in the Child of Fury part of the skill tree) in order to maximize your uptime of Rage to use your skills.

One thing I didn't realize right away that will also add an answer to the above comments.... your class is basically based on the weapon you are using, and the skills or spells only work for a certain class of weapon. This is why all characters have some sort of transfer between rage and willpower. How that works is based on a lot of factors. What I didn't know, initially, is you could have a melee weapon in your hand and use that to generate rage, dump all your rage using skills (which means you have a lot of willpower now), and with a catalyst equipped in the other hand, you can spend that willpower casting some sort of spell(s) that requires a catalyst/staff. That builds your rage back up. You can kind of go back and forth with a mix of weapon types armed, and different skills/spells on your bar.

Really there aren't classes in this game like we're used to in most games, such as Diablo. You want to be a mage.. well, throw a staff or catalyst in your hand, and you'll want to probably have some of the mage type skills learned and on your bar. You want to be a warrior? Put a melee weapon in your hand(s) (anything other than dagger, staff/catalyst, bow, pistol) and presumably have some warrior skills learned and on your bar.

There's a lot of flexibility with this game, and that's why you always see willpower and rage, vs. just a rage bar if you're a warrior. At any moment, you can go from being a pure warrior to a hybrid, just by dual wielding a sword and a catalyst (for example).. you could then go from that hybrid to an archer just by arming a bow.

I am currently leveling up my second build which is a pure brute using only rage and... it IS manageable, as mentionned, lots of tools are out there in the passives (and also in the skills perks) to help you manage / create rage! It's part of the fun finding out how to get infinite rage! (that warcry giving a speed boost generates a lot of rage on my build already, don't remember the exact name of the skill, but that's an example of how i gain rage, amongst others)