PS5/Scarlet will probably have similar power to an RX 5700 and a Ryzen 7 3700X. Probably slightly worse especially on cpu side. But yes as you point out the RTX2070 has better performance in gaming than the Vega64 while having almost half the TFlops, so while "8 tflops" might seem pretty underwhelming, it's misleading, actual performance will be anything but. But due to this you definitely might not see Teraflops used in marketing as it undersells the change.
RTX 2070 - 7.465 TFLOPS
Yet RTX 2070 performs better in games.
New consoles will perform similarly to a GTX 1080.
Actually the CPU side is what sell these console, the CPU benchmark is crazy good , it's even beat i9900K according to some forum and gaming site. Also the benchmark is actually slightly better than GTX 1080, because GTX 1080 sit around 18000 to 19000 score . And the final performance will double or more than of GTX 1080 due to low level API, optimization, and no overhead because all the spec are gaming device focus.