Opinions in this game are often people's long-term lag from earlier versions of the game. People got really excited about Willpower back when:
1. Endurance tools were less common so Willpower's having one distinguished it more.
2. Most people had less access to most IOs and wanted builds that performed well without super extensive slotting with the best sets in the game.
3. People didn't care a lot about offensive boosts.
If that's the environment you're in, Willpower is great.
But nowadays, the cost of IOs has come way down and the availability of them is way up, endurance is easier to manage, and the premium on offensive boosts has come up. In this environment, WP is kinda meh. It's fine. Almost all sets are fine. But it's not going to put together the most impressive numbers on any axis, so play it if you like it, not because you're looking for tip-top performance.