The problem with the pension company predictions, is they are based on you choosing an annuity, which most people are unlikely to do. You are more likely to ‘drawdown’ money as and when you need it.
As others have said, you have 30+ years for it to grow, which is a long time in the stock market, plus you are getting free money from your employer and tax relief. If you put just your contribution into a savings account, it would lose money against inflation.
What I would say is, when you are enrolled, log on to the pension provider website and check where your money is invested. You should have a choice of funds or lifestyle trackers. The latter will invest according to your age and drop to less risky investments as you get older.
I always chose my own funds, rather than the lifestyle ones, and a minimum of 2 to spread the risk. At your age, you can afford to go high risk to get maximum growth opportunity.
My DH (late 50s) has recently gone PAYE after many years self employed and has been auto enrolled. We did consider if it was worth it, as I am already retired and we have a large number of investments/other pension pots, plus he only intends working 2-3 more years, but….it is free money from employer, and he has other pensions that he can move ‘pot’ into when he leaves this employer.