Nothing about their advice is specific to the role of parenting itself, but more about perspective on life choices in general. If they were telling you how to be a parent, sure, but there's nothing wrong with trying to learn from each other's experiences.
Not having kids may afford some advantages in some circumstances, but in my experience, the decision is often made for reasons that most people don't see, and not just because of career goals. I know plenty of parents and non-parents, and if there's one thing I can say about non-parents, rarely is career progression a sufficient form of purpose / satisfaction in life. Most parents I know would never trade their decision to have kids for a slightly faster trip up a career ladder, but that faster trip isn't necessarily real either.
I'm in my mid 30s, and I personally will never have kids. I made this choice partially because of the environment I grew up in, where I was a defacto parent for younger siblings for most of my formative years. I love my siblings, but simply put, I'm done parenting, and have enough of my own baggage I'm still dealing with after that experience. This baggage is heavy enough that work is still a struggle. I may appear unencumbered to those around me, but that doesn't automatically equate to more bandwidth to advance my career.
I've found career success, yes, but not because I don't have kids. If anything, my career focus impeded my personal growth, so I'm working on that in my 30s.
Ultimately it's a tradeoff, and while some people may occasionally find themselves at an advantage in some way, it's unclear if this is an advantage to aspire to, or if it leads to any improvement in life satisfaction.
If there's one thing I can say, it's that work and career progression isn't really what it's cracked up to be, and isn't "enough" for long.
