35 years NI contributions is sufficient to get the full state pension. As mentioned NI is not a pot used solely to fund pension payments. It might have been originally when but is now just another source of general taxation used to fund general state expenditure.
The state pension under its current guise was introduced in 1948 following the National Insurance Act of 1946 for men over 65 and women over 60. Life expectancy then was 66 and 70 respectively. Now it is 79 and 83, but the qualifying age has only risen to 66, now for both genders.
Little wonder then that the state pension is a significant drain on overall tax revenue.