Is a bullet loan and ETF currently worth considering?

No and no again. What you say may be mathematically correct. I just don’t have the patience to deal with it. The breakeven point for this story is earliest in the last 2-3 years.

Sorry, not wanting to deal with it mathematically, but assuming a breakeven that is completely far-fetched. If you can’t imagine it, then imagine you have €10,000 left at the end of the year and have the choice between an early repayment with 1.6% interest savings or a fixed deposit with 3% interest. What would you choose then and what is the breakeven?

By the way, looking at the last 10 years of the DAX is not very helpful.

If you had just taken the trouble to look for the return triangle, then you would have understood that it’s not about the last 10 DAX years (where there was no crash), but about every 10-year period since the launch of the DAX, regardless of which start year you consider. That is exactly why the recommendation is always that equity funds/ETFs should always be held for at least 10 years to make sure they are in the plus.

Fixed deposit with 3% interest.

Where is that?

Only hypothetical, to make it a bit more understandable for Milo.

Sorry, not wanting to deal with this mathematically, but assuming a break-even that is completely far-fetched. If you can’t imagine it, then imagine you have 10,000€ left at the end of the year and you have the choice between making a special repayment with a 1.6% interest saving or a fixed deposit with 3% interest. What would you choose then and what is the break-even?

If you had just taken the trouble to look up the return triangle, you would have also understood that it’s not about the last 10 DAX years (where there was no crash), but about every 10-year period since the inception of the DAX, regardless of which start year you consider. That is exactly why the recommendation always is that equity funds/ETFs should always be held for at least 10 years to be sure that they are in profit.

You should look at that yourself. Besides, there are more negative interest developments than you portray. But yes, you better recommend such a construct where a bit more could come out. Many Americans ended up on the street the same way (retirement provisions lost, houses gambled away, etc.). With 50k he doesn’t end up on the street, but maybe loses part of his life insurance. Then calculate again and tell me when he breaks even.

You should take a look at this yourself. By the way, there are more negative interest rate developments than you present.

In 50 years of the DAX, the DAX had after 10 years
2 times with negative returns (-0.1% and -0.8%)
4 times between 0 and 1.6% returns
34 times over 1.6% returns

and after 15 years always over 1.6% returns

I don’t know where you saw further negative returns in the yield triangle after 10 years and where I made false statements about it?

Just like many Americans ended up on the street (retirement funds lost, houses lost, etc).

No, the Americans simply took out consumer debts on the mortgages of the house, and because house prices kept rising, the mortgage could be increasingly leveraged. The problem was then the collapsing real estate prices, which triggered a chain reaction.
So this has nothing to do with the topic here, because such mortgages do not even exist in Germany.

I would also not persuade anyone to choose such a construct, but I do not have to discourage anyone from taking a manageable risk if they have already thought about it themselves and are willing to take that risk. Reading your opinion, you are certainly more security-oriented than the OP and would never align your retirement provision with ETFs. I do not want to change your mind on that, I just wanted to correct your false calculation between the TA and the annuity loan.
Because of our Italian "friend" Draghi, you will only have the problem that you will be expropriated by inflation without taking risks. That is then with 100% probability a destruction of money. The 10% probability with the OP is manageable.

As a supplement, what the OP intends to do is attempted by every entrepreneur and every landlord who takes out loans. They try to achieve an overall return above the interest rate on borrowed capital in order to leverage their return on equity. This is called the leverage effect. The risk that the overall return is below the debt interest rate and thus the return on equity decreases naturally exists.