Hi
Qualified accountant here. Over £50k, under £100k as ball park of the level I was at. Worked full time prior to DC. Now SAHM to DS and DTwins. I can therefore directly compare the two.
Being a SAHM is harder. I don't have much useful spare time. Not like my lunch breaks at work, where I could walk peacefully into town, have a coffee, scroll on my phone. Yes, I'd have to perform difficult financial tasks throughout the day, which took mental concentration, but that was that. I wouldn't complain about it being difficult, that's what my "job" was. But I went to work, had to concern myself with nothing but my job and myself during those hours
As a SAHM, I mentally juggle everyone's load, all day. It's again, my "job" so I'm not complaining. All the stuff that would be shared in a 50/50 set up, I do most of. As I type this, I'm on hold to a clothes store because they've messed up DD's order, and waiting for the floor sealant I've just redone the dining room with to dry. I enjoy my days. They're harder in the sense, I don't just go in, do the specific thing I'm paid for, and go, but have to remember everything...because that's the whole point of me not doing paid employment, to do this. I have my own room which is like an office/work hub where I call the electrician, the plumber, the supermarket, the travel agent, the school, send emails, find the car we want to buy, the lightbulbs for the light that's just blown. That's before I do 5 people's laundry, clean the house, meal prep, and anything else that may have occurred. I have it all fine tuned to somewhat of a military operation. Paid employment is like a holiday in comparison, in the mental load sense...but for fulfillment, and personal happiness for our family, ours is the option I'd want every time. Our weekends are our own entirely because all the work (mine and DH's) is done by the weekend.
Yeah, we could have an extra £70k if I went full time again. It's not worth it, for the benefits we have for me staying at home, and that's both mine, and DH's opinion.