I’d have to see your list of names to see if Yabu!
My dh rejected every single name I suggested while I was pregnant with our first child. Literally dozens. In the end I stopped suggesting names in case we ran out, and said we’d wait til dd arrived.
His mother also started vetoing names, I discovered. First grandchild, she wanted in! She wanted a very traditional (and not mainstream) name to reflect her family’s ethnicity. Which I gently refused as the three names proposed were not nice.
In the end we compromised on a first name that was a milder name from DH’s ethnic roots, and a middle name I picked because I liked it - dmil then spent about two solid days researching the family tree to prove it was a variant of a name in her family tree, so that she could “get behind the choice.”
All a bit nuts if you ask me!
I think that dads and PILs don’t always feel very close to the pregnancy so naming the baby becomes a huge big deal.
I really don’t understand why, when your dp held out an olive branch and accepted one of the names on your list, you didn’t just go “fine”. Why on earth did you say “I changed my mind I don’t think it suits him.” That would have really wound your dp up, perhaps unsurprising then he refused to compromise. You’re making it sound like he wouldn’t agree to anything but it seems like he kinda tried and you refused.
You don’t really have a “right” to name the baby just because you birthed it, any more than he does just because he is the father.
I’ve never thought the first name suits my dd and almost immediately I started using a cute nn that was not even slightly associated - for example name might be Meena and I called the baby Poppy.
But over the years I’ve got used to it and of course my dd uses her real name so now I do too.
My advice therefore is to just wait - your dh will get used to your son’s real name and the nn will tend to just get used within the family.
If he tells people he’s using the nn Junior, you can say, “dp is very proud of being a dad! Me and my family use his given name, Mason so feel free to use either.” Kids aren’t dumb - the learn to respond to nn as well as real names quite quickly .