It’s complicated. As TinSoldier explains above, entitlement to the old pension and to the new one is calculated completely differently.
Just before I reached state pension age at 66, in 2021, with a 44 year NI record, and technically falling into the “new pension” era, I received a very detailed DWP letter.
This showed exactly what I was due under the new system, with all the years I was “opted out” in a local government pension scheme not counted, and what I was due under the old system, when those “opted out” years counted and I’d earned extra pension by paying SERPS and second state pension payments. All the convoluted calculations were shown.
The difference between the two was less than £5 a week, and both figures were well (over £20 a week) below the new state pension. The letter explained that under transition arrangements I would receive the higher of the two figures.
Apparently 75% of people on the old pension receive the full amount or above, whereas only around 50% of those on the new pension get the full amount.
I’m not complaining about any of this. Just pointing out the fact that those of us reaching pension age under the new scheme are not automatically better off.