@FrizzyGreenWater do you know that there are many on MN with children in a shared care arrangement of 50:50 or similar where it works very well indeed?
So whatever you think of the OP's ex, can you please not throw about unsubstantiated criticism of the rest of us?
My 9yo has spent 5 years "shuttling between homes". She's very settled and happy, and sees them as no less permanent homes than a friend who spends 3/4 weekends in a holiday cottage. I know my daughter is happy because apart from odd nights when I'm working away, she knows she has total freedom to ask to be at one home longer than the other. It's not unusual (though not common) for us to switch dates around at her request.
I know plenty of families that don't do EOW plus 1 night in the week, who make it work perfectly well.
Everything depends on the personality of the child - this child may be flexible. Mine always was, long before the divorce she was the child in the group who didn't care for routine.
OP, he is her father. 3 days may not be a bad thing. It allows her to have "daily life" with both of you, not just "Disney weekends". It may allow you a better work life balance too. If you don't have her some days, can you apply to compress your hours to work say, full time in 4 days? Then you get more time to yourself and with her.
If you truly think that his parents will do all the childcare and he'll not even be there - talk to a solicitor about fighting it.
But some lazy men actually do more parenting when they have to, and you need to be objective about whether this could be good for your daughter.
I feel for you - I wish I had my girl 24/7! But objectively, her close relationship with her father (even though it's her SM doing everything!) is wonderful for her.
So I'd also start think about how you could make it work for you.