I recently pondered this question myself and came to the conclusion that the three account model, like you have, is the way to go.
Being married means you share expenses, goals, etc, especially for the kids, the home, travel, food...
However, in this day and age, married couples don't always, or usually don't, share careers. And I think it could be argued that personal finances are part of personal careers. One person's student debt was that person's investment made in order to get the job they want, while another person's savings and investments might be a bridge to the new business or whatever that they want.
This is a selfish thought, but throwing all in would seem to stifle and disincentivize those forms of personal development and career goals. So I like the three account model and it sounds like you guys came up with a great solution that maintains that while also allowing your SO to help out.