It is impossible to have system that is absolutely fair to everyone because peopl'es circumstances can be so different. The best that we can expect is a system that is consistent, that provides for the vast majority of people, but where a few people do get badly done by.
I lost 5 years pension because I worked part time at a time when pension schemes did not expect part timers, I had a personal pension with one company which when I ceased contributing froze the amount it was worth. Shortly afterwards the law changed and such pensions had to grow with the value of the underlying assets. In 2003, the value of the pension was no more than it was in 1968, despite the assets being invested for nearly 40 years.
Things like this will happen. If someone is contracted out it means that the amount of money is invested in the company scheme not the state scheme, so being contracted out should not affect the size of you pension in total, just its ditribution between state and occupational pension. My pension comes almost entirely from a scheme where I was contracted out through out the time I was contributing.
However, people do need to accept that they need to keep themselves up to date on personal financial matters, whether it is checking their bank statements every month to understanding the rudiments of how the pension system works. For example when I married at 24 I knew better than to opt to pay the reduced married womans NI stamp, as it was then, which means I have a much higher state pension now than I would have had had I payed the lower rate.