It’s not just at lower income levels.
I’m fortunate to make a pretty decent salary.
My wife is a homemaker.
She had a part-time job briefly, but every dollar she makes is essentially taxed at the same rate as if it were tacked onto the upper end of my salary.
We get more value from her staying home and managing the household than we get from her working, unless she were to get a fulltime job with a good salary - and that has it’s own set of costs/benefits - another car, less time for meal prep, laundry, etc., plus the stress. We save more by her making all the meals, packing my lunches, and growing veggies than we would gain from her working instead.
We’re both healthier and happier and she works just as hard at home as I do at work, if not harder.
Before I was married, I did pretty well with a decent salary and investment income. After we was married, I noted the same problem: her income was taxed at my highest marginal rate.
We maxed out everything that gives us any tax benefits: 401(k)/403(b) contributions, FSA/HSA contributions, etc. If we are under the income limit, we also make Roth IRA contributions for each of us.
This substantially reduced the tax bite. Our take-home income is about the same, but we will get a lot of additional benefits in the long run.
I realize that a part-time job typically won't allow her to make 401(k) or HSA contributions. But, she CAN make an IRA contribution (Roth or traditional). If you can invest that additional money in long-term plans without making too many sacrifices now, you'll come out ahead.
The conversation came up at tax season with our estate attorney that we might consider a "legal divorce" in order to reduce tax basis by filing separately.
Pretty damn sad when that conversation comes up.