As I said, if you pay into a pension, any pension, for every 80p you pay in the government gives you an additional 20p in tax relief. So £1 goes into your pension pot.
Any other savings accounts the government does not put that 20% tax relief into it.
You could do as you said and save into an ISA or something, then buy an annuity with that pot of money at retirement age, instead of with a pension pot. But you wouldn't get that tax relief of 20%.
The advantage of your suggestion is you can access the money for other purposes at any point. So if you're diagnosed with terminal cancer, for example, you could spend your ISA on additional treatments not available on NHS or just spend it doing your "bucket list" before you died. A pension is locked in there and you can't access the money until you're 55. So it's a gamble. Are you likely to need the money for purposes other than a retirement income or would you be better off with a pension and getting the government putting 20% tax relief into it.
This tax relief is nothing to do with whether the interest on savings is taxed, which I'm wondering if you're getting confused with that since you mentioned ISAs. The interest made on an ISA is tax free. With any pension the government literally puts money into it for you, that's what the 20% tax relief is. That money then accrues interest the same as the money you put in. If your employer is also putting money into your pension that's even more free money going into it, meaning a bigger pension pot upon retirement. Your employer wouldn't put that money into your ISA instead.
This is a completely separate situation to comparing whether a private pension is a better deal than an employer's pension. The employers one is always better than a private one, if they're contributing to it, regardless of whether it's a defined benefit pension scheme or anything else. The "defined benefit" part is yet another additional beneficial component to your friend's pension scheme.
Sometimes you'll get an employer offering a pension scheme but not paying into it themselves. In that scenario it's no different to you paying into your own pension scheme that's not offered by the employer. If the employer isn't even paying into it for you (because they're stingy, basically) it's unlikely they're offering additional benefits like "defined benefit" or "final salary" or anything else.
You're comparing whether you should pay into a savings account or into a pension like your friend's one. You need to strip it down further because that's not a good comparison. For a start, to have the opportunity to pay into a pension scheme like your friend's one you'd first have to have an employer who offered such a scheme, which might mean working for a different company or changing careers altogether. What you need to decide first of all is: do you want to pay into a pension (any pension) at all, or do you want to save the money elsewhere. You need to decide what matters more to you: getting the 20% tax relief that paying into a pension gives you, or having the ability to access the money at any time because it's not locked into a pension.
In simple terms, if you had a pension scheme and a savings account, both invested in the exact same way in the same companies and performed the same, and if you put a £30k (random figure plucked out of the air) one off payment into both of them and left it there to grow, at retirement age the pension would be worth more than the savings account, because of the 20% tax relief that went into it and grew alongside your £30k. The effect of the tax relief is how the government rewards you for choosing the pension and locking your money away until old age.