His holiday time with his dd is also being taken away from him by you...
And he's thinking, I only get every other weekend, holidays are my chance to really spend some quality time with dd doing all the things we don't usually get to do... In much the same way you are thinking you have lots you want to do with her and you won't get to spend any time together...
Neither of you is automatically entitled to half (or more) of the holidays. Your dd is the one with the rights here, not you and not your ex. She has a right to a relationship with both her parents.
Reasonable people would look at each other's point of view and work out what is best for their dd, not what they want! If you can't agree then a court may order half the holidays, and trust me you want to avoid court if at all possible!
So yes half the holidays seems like a good starting point, especially as she only sees her dad every other weekend in term time. So ask yourself if you're be happy to settle for half the holidays (you already said you're not). And then ask yourself that again thinking about if you only saw her every other weekend, like her dad does... You'd be wanting for as much holiday as you could too and getting angry at your obstructive and non-understanding ex and demanding your "rights" too no doubt!
If you can then show that you have valid welfare reasons why she shouldn't spend half the holidays with him then lets hear them. Because otherwise the reasons are because it's what you want. Well sorry bbut what you want and what your ex want are secondary to what is right for your dd. And spending time with both her parents is right for her. So be fair and split that time fairly and equally.
So your question should then be how do I split the time fairly...
What specific things are you planning on doing with your dd? Have you booked to go away somewhere? Has your ex? If so then you should factor those into how you split the holidays.
How much time can you both get off work? Does he or you have extended family who are hoping to see dd over the holidays. If they are limited as to when they can visit factor that in to the split.
Some people do half and half exactly (ie first 3 weeks with one parent, 2nd 3 weeks with the other).
Some people do 4 lots of 10 days and have two of those each. So you get 2 long chunks of time each.
Some people alternate a week at a time.
And some people do various combinations.
You have to factor is how far apart you live, so how much travelling your dd will need to do between homes.
Try and come to an agreement. Because you will find yourself with a court order otherwise and then there won't be any flexibility.
It is hard I know, but you have to share your dd. I'm sure you would want the same if she was living with her dad rather than with you...