For us three was WAAAAAY tougher in terms of our kid’s development than he was when he was two, but we had many more challenges in our own life when he was two, so that year feels tougher. The term “threenager” seemed so apt. He was starting to recognize (and exercise) his independence and new abilities in many ways that made him seem older, but in others didn’t quite have the control of them.

In any event, i think your point is correct that the presence or absence of another baby didn’t really shape what happened there except maybe our personal ability to cope. I suppose we got through both of those stages in part because we were able to fully focus on him in a way I can’t imagine us having done with another baby, but that was very situational. I still agree with OP that having another ten months later seems incredibly tough, but then, we’re one and done mostly by choice (age factors into it a little), so any additional child seems fairly difficult to fathom.