Switzerland has a bit unique position within Europe by having the highest salaries, so plenty of folks retire to places like Spain or Italy (or Bali) where your Swiss pension can give you relative luxury lifestyle compared to not so great lifestyle back en Suisse.
Generally everybody in Europe wants to have Swiss pensions, not only for the amount but also for the 3-pillar systems where you actually save decent amount for yourself to live comfortably and/or retire early. Not the case in most european countries AFAIK.
Any form of retirement works the same - young people working to serve the old. How you finance it is a different question - but clearly increasing taxes & lowering pensions is just one way of the system breaking down. Another way is, everybody saving while working, not having kids, then spending when retired (results in market crashes & massive inflation).
The original problem is not having kids. The “direct transfer” system simply keeps incentives more aligned.
So you need a pension system for a population that doesn't grow. Basically that means that everybody has to pay for their own pension. It doesn't really matter whether you do it as taxes that get paid to the people currently retired or by saving money.
The solution The Netherlands came up with (next to moving to an individual pension system) to try to raise the retirement age to 67. This is quite unpopular. But it's either that or a low pension.
Pension isn’t about money. It’s about work. Less working adults => less surplus value created by society => less resources available for retired people.
How you finance that - via direct payments / taxes, or via individual savings - is besides the point. Neither of these can defeat the economics of supply (of working-age adults’ labour) and demand (of the retired non-producing population). If you try to force it, you’ll just cause other issues (e.g. housing / market crashes caused by all pensioners cashing out at once, or wage/food inflation caused by labour shortages).
Pensioners don't cash out at once. The number of pensioners grows slowly which many result in gradually lower demand for stock or real estate. No need to expect a crash because of this.
No need to expect anything to happen to food either. Food production is highly efficient and relies on only a tiny fraction of the total labour
Blindly investing and then assuming that it still has value when you retire has a lot of risks. This sometimes happens with owners of small shops who hope to retire with money they get from selling the shop.
Other European countries (not all) have similar pension systems that you describe, with same problems, and even though they don't have the Swiss direct democracy, they have been equally unable to change their systems.
For example, the Swiss pension system is similar to others in Europe, where the current working population pay taxes almost directly towards pensions of the retired. Since this system will break down if taxes aren't increased like crazy or pensions lowered, politicians have been trying to change the system. But there are too many people soon to be retired or already retired that care less about their country's youth and future than their own pension, so they keep blocking changes. So every democratic system has its tradeoffs...
I learned this from a young Swiss when I was visiting Switzerland and praising their way of democracy. It was a few years ago though, so maybe this info is no longer accurate. And I didn't fact check, it was just an example brought up in casual conversation.