As was said, it’s in comparison to something else and as a result he’s actually not a lot more effective than people give him credit for.
This is a game about loot. Things are often measured by the rate at which any build can make loot fall out of things. Zane is… Very slow.
To some people that makes him unplayable because any benefit he brings is totally overridden by his inability to achieve the ultimate goal of the game - get loot.
You aren’t wrong. They aren’t wrong. You just have different opinions. Each of you are giving him the credit he deserves from your own perspectives.
I assure you, this is quite normal.