I think it's really unkind of your Ex-H.
FWIW my best friend has 2 DD's, her DH has a DD from a previous (very short) relationship (he didn't know she existed until CSA letter turned up!). His DD mum has remarried and has 2 more DD's. The girl calls both of them Dad.
She vists every holiday as lives too far away for weekly contact.
Every year when a holiday is booked they include his DD. Mostly its been 1-2 weeks in UK cottage somewhere near a beach. She goes on holiday abroad with her mum and SD and sisters every year as well. Last year friend and her DH went abroad and offered to take his DD but she couldn't go as she as went abroad with her mum etc and it crossed over. Friend and DH couldn't rearrange as he couldn't take his holiday another period.
This year friends DSD has said her mum etc isn't going abroad this year as no money and she would love to go with friend and her dad. Thing is friend also not going abroad due to money and no plans for UK trip for same reasons. Friend and her DH are feeling really guilty as they think they should take her abroad as she didn't get to go last year.
Lot's of pople think my friends DSD gets a great life with 2 holidays and 2 families providing gadgets etc but its really hard for her.
And for those saying OP' DD may be whingy and demanding at her dads my friends DD's are the same when my their dad spends time with his DD, and worse if my friend does.
I really don't understand how anyone can justify what OP's ex has done. This isn't even his own children (with DW) being put before his DD, it's her children.