At the start of NEM, they just get 5% but you will get 45%(if you will put 45m to you).
45m is less than 5% of the total 1 billion.
Mining has no relationship with proof of stake.
If you want more stake, then I suggest that you exchange Nxt for NEX.
A lot of people will complain if more stake is given to people who did not pay in. So there is a balance that needs to be preserved.