Hello! interesting discussion! And It makes clear some details!
Concerning plants: Salvinia minima and Ceratopteris grow very quick now in my tanks, but even extrem faster if I put them afterwards in a tap water tank of someone else.
Soil, and Co2 plants ( I never used them) are for me an Armamo thing. Very large tanks with many plants and very, very few little fish.
Our small tanks without water change is for me like being closed in for months in a small room without fresh air!
And as Pawel writes, we don’t know what substances will increase in the water after some time. Our fish are specialists in an ecological corner with a very special, super-clean water…