AIBU to think my DH has gone mad over this baby name?

No, so sorry OP it's awful as you already know. She will be judged all her life with a name like that! You're giving birth so you get the last say. [DH and I had an agreement - I had the last say with girls and he with boys.] Luckily we had 5 girls but we still managed to agree on names for each of them. Best case scenario would be letting him have it for a middle name if you really must.
I'd show him this thread OP.

That’s peak chav. I know people with that name and everybody I know who named their child that is ghetto af.

I support you. Tell your DH he is being ridiculous.

Find the next name on the Top 100+ names that you like, after that abomination, and suggest that. He can't argue it's too popular as it's less popular than backwards Heaven.

Awful. Just for a start, nobody will know how to pronounce it, and she’ll be asked for evermore how to spell it.

How is it pronounced? Like Never?

It's a pain to have a name that people can't spell or pronounce. Sorry. I have another Irish name which is equally challenging.
It's just tiring, every phone call to bank or utiliities, dentiste, hairdresser etc, autocorrect keeps changing it, lifetime of.mispelling.
Just veto the name. He vetoed yours

It’s an awful name and I cringe every time I hear it. My friend is a neo special care sister and they all inwardly roll their eyes when they hear it. Like your husband the parents think they are choosing a unique unusual name, but it’s more common than you think.
Honestly stand firm and tell him absolutely not.

Also it’s not remotely unusual nor unique.

Yes he is unreasonable and it’s known enough name, not very widespread but not unique either you just need to google.

Dying from laughter at yours “I suggested even Freya” 🤣🤣🤣

It’s already an issue in many places in the UK, and it’s waaaay worse outside of it. Unfortunately it bears no resemblance to the way those letters are pronounced in most languages. It will most likely mean a lifetime of correcting people if she ever goes abroad.

Or Genna - that’s heaven in Maltese.

I can't believe no-one has just suggested the classic MN "LTB".

I live in an area where Niamh is the most popular spelling but If you're worried about people pronouncing Niamh there are alternative spellings Neve, Nieve, Neave, Neavh or Neeve.

It's very common. And has a stupid "meaning".

I don't think there is a class in a British primary school that doesn't have a Neveah (yes a and e other way round, but same name?) If you don't like it and think your DD will not thank you for calling her this, then say no. It is not unique at all and if it is spelt heaven backwards, she is always going to have to spell it out too.

I can remember having real problems choosing a name for our daughter - I endlessly scrolled through name lists (eg the 50 to 100 most popular names) and sent ideas to DH only to have them rejected. You will find something you both like in the end tho'.

Not a fan, Every time I see that, I just think of the shop in the season 2 of the Netflix Show ‘You’ which was named that.

And if your DH wants his daughter to have a unique name he’ll get a better chance with Ruth, Carol or Karen. I suspect these names are practically extinct in under 18s.

Went through this with dh. Couldn’t agree. I just kept throwing names at him until we found one that both of could compromise on. The name we picked he loved, I liked. You both have to agree.

We have a Gaelic name for our child that is completely un-phonetic. We both love it. Yes it's often mispronounced and misspelt initially, and when I give the name I always spell it out. But teachers get it right. We love the name so much I think it's worth it. Maybe our child will feel differently when older or maybe he will love it too, no way of knowing. He has a straightforward middle name that we also love in case he wants to change it.

(Btw I have a relatively simple first and last name that is somehow always misheard so I always spell it out too. 🙄)

He's turned Sophie and Amelia down for being "too common" and his choice is Nevaeh.....? 😬

Heaven backwards? Cringe. Like a dreadful cheesy pickup line.

Lucky he didn’t pick Lana.

Maybe he might like a palindrome - Hannah is lovely…

Sadly I'd say yes, it will be endlessly mispronounced. Sister's daughter is called Sian and she was announced at her graduation ceremony as Sigh-Ann. If people can't get Sian correct, they'll really struggle with Niamh sadly, it's a beautiful name.

50 really isn't old you know. I'm not sure what pension forms you think 50 year olds are filling in in your imagination but it's pretty ageist. State pension age is 67.

Anyhow, it's an awful name. Niamh is nice though ( pronounced Neve)

There are better girls names with a heavenly meaning if that's what he likes.

Celeste
Celine
Lani
Diana

Your friend comes home from working with very poorly newborns and parents going through hell and takes the piss out of the names of the kids she looks after?

I have less issue with the name and more issue with the sort of person who does that while in a position of trust and care.