I would suggest using the word parenting instead. Saying that motherhood is a full-time job kind of implies that the father shouldn’t equally share in the parental responsibilities of raising the child. That’s a mentality that society needs to break out of.
I think it’s also fair to say that parenting can be a full-time job, but that doesn’t necessarily mean it is for everyone. It just depends on what kind of parent you want to be. I was raised by a parent who didn’t work, who did maybe an hour of housecleaning a week, and whose duties as my “personal chef” amounted to sticking some frozen chicken nuggets in the microwave for two minutes.