Well then my problem is more that a console doesn't have to have good post-successor sales to be "long-lasting". A console that is still selling 7 years later is better lasting than a console that dies after 5. Regardless of when the successor came out.
PS consoles are incredibly long-lasting, this is a fact, post-successor sales are irrelevant to this statement because it's the wrong metric to use.
"post-successor sales are irrelevant"
No they are not, a console that is better selling will generally have much longer support before a successor is introduced, so just looking at the years doesn't present a whole picture as that is going to be mostly indicative of just consoles that have sold well in general. I mean, if we really were to split hairs then Nintendo would probably have one of the highest post-five year sales for consoles because of the Gameboy and NES. Yet most people consider Nintendo the worst when it comes to sales longevity because of the Wii and Gamecube.
Anyway, to the point, it is an important consideration when predicting the lifetime sales for a console. If the PS4 had post successor sales as great as the PS2 it would end up at approximately 160M and be THE best selling console of all time, but the second that a PS4 successor was ultimately revealed sales dropped dramatically (despite 2019 and 2018 still being fairly decent years). It isn't the wrong metric to use, it's A metric to use. Everything is considered when predicting sales, including the length of the generation. With the PS1 and PS2 the length of the generation didn't really matter. With the PS3 and PS4 though it ultimately did. Therefore, it is accurate to say that the assumption of Playstation consoles should be changed to more accurately predict lifetime sales in the future.