@caggie3
You are massively over-thinking this. Only on MN have I seen drama re what's app groups. I've 3 DC, once what's app started being used, it transformed my life (kids-wise at least!)
I could quickly check re announcements, homework, organise parties & play dates & teachers' collections. I'm a single mother, work f/t, so massively helpful.
For some classes, we used them to arrange mum meet ups too, it depended.
I've never seen anything remotely bitchy or dramatic, just boring child info!
While yes, it should really be both / either parent, invariably it's mums. I agree with your DH & can't understand why you wouldn't join.
Then again, I also get perplexed by the decided 'only here to drop off' school of thought on MN. I don't have friends at the school gate, and I do just drop off as I'm always headed to work but I enjoy being able to have a quick chat with other parents when opportunity arises. I can't imagine thinking about it much more deeply.