I think many people on here, and it's a bit of a generalisation to say woman, but the majority of sahpS are the mother, similar ish idea with the smaller deposit, or are eventually the Person to give up their career. My opinion is that a lot say, no I wouldn't settle for that arrangement etc.
However I often wonder if the table was turned and they had the 300k deposit would they then be wanting to protect it?
Personally I feel that of it is that uneven then a fair compromise is too protect your investment for a number of years or until children occur etc, then it's fair to be 50 50.
Again 90% deposit does it equal ownership, who will lay the mortgage is important for you too?
I think of it as, if say 3 years later you wish to sell and split, then take the value of the house increase, say it's gone up (or down) by 20%. So eg
Cost 650,000
Your deposit 30 000
Dp deposit 300000
Mortgage 320 000
Now worth 780 000 with 280 000 mortgage left
Leaves 500,000
Your deposit plus 20% increase now equals 36,000
Dp deposit plus20% value increase = 360,000
This then leaves 104,000 profit. This is split 50:50. So 52000 each.
Thus reflects your dp's bigger share originally but also reflects that without each other neither of you would have had the house to benefit from. So the increase in value reflects you both.
I think it's very fair.