No, whoever doesn't want another child calls the shots, whether it's the dad, the mum, the breadwinner, the lower earner or the SAHP. Because having a child is a massive, life-changing deal (and no, not just financially, in terms of time, energy, emotionally, in terms of the attention you can give your other children, how having a younger sibling will change the activities you can do with your other children, the support you can give them, hundreds of things, and children should not be brought into the world with a parent who's going to resent their existence. And of course the physical/health aspect for the mother).
So, you were the primary earner and you said no more kids, and that decision was the one that held sway (rightfully). But say if you were a SAHM and your husband wanted more and you didn't... you think his decision should have trumped yours because he earned more? And you should've been obliged to have another pregnancy you didn't want? Absolutely not! Or if you, as the breadwinner, wanted another and your husband said no? Do you think you should've had the right to override him and have a child he didn't want, because you earned more? Clearly not.
It's also a bit strange though how you view family finances... as though the one earning the money is the only one who would feel the financial strain of a third child..? The entire family would experience the financial strain, from the children having to give up clubs and wear second-hand clothes, fewer holidays and a downgrade in the level of Christmas and birthday presents they used to have, to the SAHP having to budget very carefully at the supermarket, go without treats, clubs and classes, clothes, nights out etc., perhaps have to walk and take the bus everywhere with all the kids and shopping because the family can't afford a second car... It's very bizarre to talk as though the one earning the money is the only one affected by the family's finances...