Exactly, the whole thing is no longer helpful. One can only assume how it currently looks and then estimate how it should look in 5 years and whether that is even remotely realistic.
Obviously, but does that make a difference to the feeling of living there?
Are you allowed to use more rooms because of that or differently?
For me, it doesn’t feel like it matters whether I actually own 20 or 30%.
However, I am about 5 years earlier in my own home, can design the garden, and have the stress behind me in younger years or before having children.
That’s why I also wrote that only the OP can decide that alone.
However, financially, waiting rarely leads to an improvement in the financial balance, or only with an extremely high savings rate. Ten years ago, there was still the possibility of lowering interest rates, but that option is now almost fully exhausted.
That is simply “being stingy is cool” put differently. The difference is not feelings, but your security and that of your family. Suppose you become unemployed after five years, then it makes a significant difference how much percent you already own. In the best case, you sell the house and pay back the loan plus prepayment penalty from the proceeds. In the worst case, which can still occur after a long time with zero equity combined with low repayment, your house sells for less than what you owe and you become insolvent and completely ruined.
That is the only reason for equity, not the differences in interest rates. Everyone has to know for themselves how far they can look into the future and assess their risks. But with 100% financing and a laughable 2% repayment, everything must go very well for a very long time. This risk is the real risk of construction financing, not the theoretical interest rate risk at the end of the initial term. There you might lose a few thousand euros, which inflation has already long since offset.
With regard to the OP, this does not apply, as he has 100 - 120 k€ of equity and, in an emergency, possibly support from the family. I also specifically wrote somewhere that I would not recommend 100% financing, but in this case saving not only makes sense but is necessary.