I have always opted out of pension schemes, all my life. When I was a single parent I could barely afford to live and still ended up with debts just to pay the bills, so no, a personal pension wasn't an option for me. I needed every penny I could muster just to survive.
Years later, I don't regret any of it. The one job I ever had which paid well and gave me more money, I still opted out and went travelling with the extra cash instead. I'm extremely glad I did it, I had some amazing travels which I certainly couldn't have done if I'd waited until I retired, I'm too frail with health conditions these days.
I'm not long off retiring now and I'll only have my state pension when I do, but I have everything I need and will be able to live off the state one. I don't own any assets - I rent and have a lease car - but I will be able to manage on the state pension. My current job is part-time and in a low-paid sector, and I earn about the same as the state pension per month, so I already know I will be able to survive in retirement.
Honestly, it depends what you want out of retirement. I am always surprised by these people who have huge pension savings, what are they planning to do with the money?? And, like you OP, I also had relatives who put everything into a pension but died just before retirement age so they never got to enjoy it anyway.