You misinterpreted my thought experiment. In essence, if you didn't buy time, you'd have an extra 75k that you DIDN'T spend on buying the years (and yes, whatever you earned in the meantime). If you bought it, you'd have 75k less in the bank (cause you'd have spent it on buying those years).
So now pretend you are at age 42. Would you rather retire right then, and have 75k less in the bank than you could otherwise (because you spend it on the pension), or would you rather work 6.5 more years and have that extra 75k (plus, yes, whatever you make in the meantime - irrelevant for this comparison).
In any case, the reason why I said it may not be correct is that it's much too simplified. This is a much more complex question than that.
I have the option of buying years on my pension, as does my wife. We also have the option of taking them early (at a penalty per year that it's taken before fully eligible).
I have a spreadsheet with about 15 different scenarios (buy years versus not, retiring at various ages with and without the penalty) that graphs the break-even times for given rates of return (I.e. retiring 5 years earlier gets you more money sooner, good if you die earlier, but if you wait and retire later, you could catch up to one extra years of payment with the higher amount). So one scenario is better if I project we live until 75, another at 80, etc. etc.
Plus my pension has a COLA and kicks in and increases different percentage amounts after certain years, so starting that earlier is also nice, so that's taken into account in the spreadsheet.
And, of course, the better the return on money taken early the better taking it early seems.
In any case, it is certainly going to be a highly individualized decision. To purchase the years for myself and the wife it'll cost ~75k. Probably going to do it, and retire 10 years before eligible, based on the curve I prefer the most among those graphs. (FWIW, I plan to be FIRE long before taking the pension, even with taking it 10 years early, so it will in no way affect my ER date.)
Your mileage will vary quite a bit, most likely.