Is 4 kids easier than 3?

We are on our 3rd baby and my husband is getting a vasectomy soon. I've seen all the articles saying 3 is the hardest go for the 4th. Some family and friends saying the same. My husband agreed on only 3 kids before we even got married. Originally i wanted 4 but I'm a stay at home mom and can't wait to get back to work when all the kids are in school in another 3 years. Will having only 3 always be harder than going for the 4th? Would like to hear from mom's of 4 kids or 3 kids.... What's your take? Feel free to comment your experience.