I do not know if it is helpful or adds more confusion, but I just wanted to share a recent whitepaper (mainly section 6), from IEA Task 61, that is sort of related. It proposes a system characterization for different performance metrics/simulation methods: https://task61.iea-shc.org/Data/Sites/1/publications/IEA-SHC-Task61--Technical-Report-C2.1-Whitepaper-BSDF.pdf