I'm in the YABU camp. Does luck play a part in people doing well? To some extent yes. But I think to say it's all down to luck really diminishes the effort some people make to overcome the hand that luck, genetics, ancestry and whatever else gave them.
I haven't paid my mortgage off yet, but I'm late 20s with a good job, good wage, progressing well etc. But most of it isn't down to luck.
I'm fairly intelligent - guess that's lucky. I also met a nice guy and married him young, and one of his parents is supportive and helped out with his share of buying a house, so i guess thats lucky too.
But on the flip side I grew up on a rough council estate where drugs, teen pregnancy and crime were endemic and a life on benefits was a norm for many. Of the 30 kids in my primary school class only a handful had a working parent. I grew up in a single parent household with a mum who drank and smoked a large propionate of our income. When it came to choosing high school I said I didn't want to go to my catchment school, looked at league table in our local paper and asked my mum to apply for another school. Luckily I got in as my local school was truly dreadful.
I worked bloody hard at school, plus worked multiple part time jobs from when I was 15 so that I could afford to go to school, have uniform and clothes, pay to go to uni open days and interviews. Got in to Oxford. Then got thrown out and ended up in a council flat at 17 starting from scratch. Couldn't afford Oxford, got a full time job and applied to uni locally and proceeded to work full time while doing a full time degree - which meant I graduated with a 2.1 instead of the first I was capable of but also meant that when I applied for competitive graduate roles I did well because I had better experience. Im taking incredibly hard professional exams. I've taken roles requiring travel and working away from home even though I have dd because it helps to build my career. I've been through redundancy, workplace bullying etc. I only have one child because I get very ill when pregnant so having another could be very damaging to my career so I have to plan timing really well before having another. I've been injured in an accident and had months off work, DH was injured in a car crash and had to give up his job and start from scratch. I'm also autistic.
I don't think I've been especially lucky or privileged really, and so it annoys me when people say it's all down to luck because there's often more to it than that