If a PS6 Lite is launched in 2027, it will likely replace PS5 as the new entry point to the ecosystem. But even in this scenario, the PS5 has a good chance outselling PS4, because PS4's production fell off a cliff several months before the PS5 launched. For a plethora of reasons it's highly unlikely for PS5 to repeat that, but I don't know if it would sell enough to close the gap before high volume production ends.
PS4 sold 13.6 million units in FY2019, and a measly 5.7 million in FY2020. PS4's sales never reached their true potential (130 million+). Production was abruptly cut and Sony suffered over 3 years of shortages starting from around March 2020. PS6 won't see a fraction of the demand levels the PS5 had in early years. Sony's ecosystem is no longer tied to their latest hardware, which is favorable for PS5.
