yes, the energy is guaranteed to come from biomass (gas production from household waste etc + biomass cultivation on landfill sites)
Guaranteed refers to the supply contracts. There were cases where the renewable share was sufficiently fulfilled by mixing biogas with natural gas. After reviewing the supply contracts, it turned out that this mixing was not guaranteed or assured and could be changed by the supplier at any time ad libitum. Therefore, this construct was not accepted as proof.
...consequently, only the chosen insulation/windows would determine whether my house becomes kfw70/55/40 ?
Probably (all exterior components). However, it becomes increasingly difficult to meet the Ht value with better efficiency status. For example, if a building is just below the respective limit, there are other possibilities to still achieve the value. However, I do not want to name or comment on these here.
Basically, it is never wrong to achieve a high insulation value of the building envelope, because the best energy is that which is not needed.
It makes little sense to compensate a high demand primarily or exclusively through system technology. With low demand, on the other hand, one can perhaps "afford" somewhat less efficient system technology and save investment.
Best regards.