"an amazing husband"
Technically, ممتاز translates to "excellent," whereas "amazing" would better be rendered as "رائع." To amaze is to fill with wonder or surprise, like راع in Arabic, and to excel is to surpass others and be better than them, like امتاز in Arabic.
You're right, but I'd say and even more accurate translation of "amazing" would be مُذهِل or مُدهِش
Having said that, I think the translation is trying to avoid literal translations when they don't make a lot of sense. The English sentence isn't trying to say that the husband fills with wonder or surprise, it's just trying to say that he is really great, and the Arabic sentence is trying to reflect that, too.
Nope. الذهول and الدهشة aren't just a sense of wonder, they're a sense of delirium and confusion, so "astonishing" or "stunning" or even "marvellous" would fit the bill better.
"Amazing" in English does carry that meaning, that the husband fills with wonder or surprise, so if the husband is just really great, "excellent" should have been the translation used. "Amazing" sounds too evocative a translation for an emotionally neutral word like mumtaaz.
Following is the Cambridge Arabic dictionary translating “amazing” as مذهل while simultaneously translating it to English as “very good”
Also, please read the section “Can amazing mean good?” in the Merriam-Webster dictionary explaining how the modern meaning of “amazing” has been watered down and stopped having its original meaning and strength here: https://www.merriam-webster.com/dictionary/amazing