Well, he was a sprinter. I don't think he ever performed well as a roleur and I don't remember him being able to get away on the hills either. He could follow, but getting away, no.
Zabel could win in a variety of sprints, flat, uphill or after a rolling stage, a 90s version of Sagan in sprinting terms except better on the flat finishes. A sprinter winning Amstel is no mean feat, especially defeating the defending champion Michael Boogerd who was definitely no sprinter. Zabel wasn't an attacker, but why would you if you could hang on over tough courses and then use your sprint.
I find it strange to see the suggestion that Zabel is undervalued because he was a sprinter when you see the amount of fawning over Cavendish, who is far more limited than Zabel as a cyclist.