I've been with my DH since high school so over 25 years. Basically I have never been a single adult.
By your friend's measure I should be a gibbering wreck on my own.
My DH travels with work sometimes for extended periods, leaving me and the DC at home.
I have a successful career and could, if necessary, pay all the bills on my salary.
I can manage the children on my own for weeks at a time without any problem or help.
I can deal with all the household maintenance and finances without needing any help.
I am happy in my own company but am lucky enough to have a great circle of friends.
I adore my DH, he is my best friend and God forbid something happened to him I'd be devastated.
But, I have no doubt at all that I'd pick up the pieces and build a new life on my own.
Independence isn't about experience IME, it's about attitude. I have several friends who!ve been single for long periods of their lives who can't cope on their own with the children for a weekend, or who don't understand the family finances, or who can't bear to be at home alone on a Saturday night.
Your friend is wrong. I truly pity anyone who believes that not having one person in your life who you would miss if they died is a better way to live.