No at all. I'm saying IMO people in general/ children should celebrate their mother (rather than celebrating their wives for fulfilling the role of a mother). It's not that difficult a concept to grasp. You feel differently. That's fine.
I don't think I said OP should be left alone all day. I'd have assumed women would spend the day with their own mothers if they are still alive and they get along, or in the best case scenario work out a compromise that works for everyone like you've done.
Obviously a baby currently is too young to celebrate their mother. That's ok. They'll be able to as they get older.
I'm allowed to have a different view to you and to offer my opinion when OP asked for opinions in AIBU.
It isn't disingenuous to have a different opinion. To suggest otherwise is daft.
This is the crux of it and what personally I don't agree with: "If that is not possible due to distance, and the baby is unable to spoil their mother themselves, then DH should be prioritising his wife’s experience over his mothers."
I feel Mother's Day has morphed into something where her DH now has to prioritise his wife on Mother's Day - i.e. celebrating his wives for fulfilling the role of a mother rather than his mother.
Couples have baby's first everything to share together, wedding anniversaries, birthdays etc. It's just one day for your mother and it shouldn't stop or be overridden because you got married and had children of your own IMO. If you think differently, that's fine. It doesn't make me disingenuous.