The "bratty" step kids: did they wreck your marriage?

There are so many complex familial constellations today, it’s a wonder anybody can keep track of the relationships anymore. With more and more people having second and third marriages (fourths and fifths too!) it should not come as a big surprise that at some point one could find oneself in the “step mom” role. From what I hear, this can be a quagmire of epic proportions.
Couples tend to fight over kids even when it is their own biological children. It is usually a power struggle, and one parent feeling that the other is “usurping his authority.” Let’s face it, we still live in a world where the mom plays the role of nurturer and main care giver to the children in greater proportions than fathers do. But we also live in a world where more fathers are taking a more active role in the rearing and everyday care giving of their children. It is a beautiful thing to see and to watch, but it also seems to create more conflict in the home than when dads were more focused on working outside the home, bringing home the bacon, and leaving the children to mom to do with as she may.
So, now, you have all these disagreements: play dates, medical care, after school activities, school – private vs. public, discipline ( a big one!), manners, bed times, shower schedules, and a host of other things.
Now compound that with the fact that one of the parents is not the biological parent of the child, but only the step mom or step dad, and figure out how this dynamic amplifies these fights, and could even lead to the tipping point for many relationships.
What often seems to happen is that the step parent feels like a stranger in his or her own home, and interloper not only in the family, but in the marriage! She or he may feel that they play second fiddle to the kids, or god forbid, to the ex-spouse and biological parent of the children who probably can still push important buttons. Usually, it’s the ex wife that can do this. She has a way of making her ex husband crazy, and then he comes home to his second wife, and their relationship is affected by the things his first wife does or fails to do. No woman wants to feel that another woman can “make her man crazy.” So right there, you’ve got big problems.
And I will say this personally: when a man is really into his children, if his new woman or wife does not “get along with them,” that relationship is all but doomed. So the trick to me is, before marriage, to ascertain that the relationship is sustainable. You can’t marry with your eyes wide shut. One has to spend time, while dating and getting to know someone, in the presence of the children. And observe! And take mental notes! And don’t sugar coat things and try to make them into what you want them to be. Face the facts. Act accordingly.
If you don’t agree with how he disciplines them while dating, when married and living together with him and the kids (sometimes he has custody!) it’s only going to get worse. Much, much worse. In this regard, you are most definitely not going to be able to change him. Men cannot be changed, girls. Please understand this fundamental truism. Alright?
As a general rule, bratty kids don’t become bratty after daddy remarries. They are either bratty or they not, before marriage and after marriage. It is the new person coming into the relationship that has to figure out whether it is a situation they can handle.
On the other hand, it would be nice to have a spouse (husband!) who puts you first, and makes EVERYBODY, including the step kids, understand that you come first in his affection and in his life. If you don’t have that, you could remain married for 100 years, but you will never really find true happiness.
It seems to me that for a marriage to be successful, both parties have to be willing and able to put each other first – above the kids, parents, job, friends, hobbies, addictions, ex, everything. Or they shouldn’t marry each other because the marriage will never work under any contrary set up.
Am I right or wrong?