There's nothing incompatible with my post and your quoted source.
The 'inter-generational transfer of wealth' is true in two respects, neither of which means SS is not an annuity investment combined with other financial products. Rather, the "inter-generational transfer of wealth" describes the manner in which the annuity company (the US govt in this case) funds annuity benefits.
1. The first SS/annuity beneficiaries received full retirement even though they had not been paying in. They couldn't, the program had only been started when they retired. Thus, their benefits were funded by younger workers. I.e., an "inter-generational transfer of wealth". They got what they never paid for (or invested in) and that came from younger workers. This was a 'one-time' occurrence and has long passed.
2. Current benefits are (mostly) funded by current contributions. So, in a way, one can say it's an "inter-generational transfer of wealth". I would personally disagree since many retirees don't receive more than they paid in (invested), and for most that do the ROR would be abysmally meager. Simply put, the cash flow arrangement utilized by the annuity payer does not work to define program, merely defines the payer's practices. E.g., if I invest in a bond and am paid 2% interest, the fact the bond debtor stole money to make the 2% payment doesn't mean I'm a thief.
SS will never bankrupt (or, if it did it would be the least of our problems. I.e., it wouldn't matter a whit.). Worse case scenario, no money in the trust fund, no fixes, no improvement in the economy etc, benefits will drop to 70% of promised levels. Hardly good news, but nothing close to bankruptcy and zero benefits.
Bankruptcy and zero benefits would only happen if no one was working. If no one is working there's nothing to buy, no food, no electricity etc. anyway. If that happens the fact that SS is bankrupt won't matter. Won't matter if it isn't bankrupt; where are you going to cash that check (nobody employed in banking) and even you could cash it, what would you buy?
Fern