What sustains it?
Halo and Halo 2 sustained the original Xbox, games in the same hierarchy as Persona, other Xbox games had poor sales yet sold 24 million in 4 years.
What sustained Sega Genesis ? Sonic and the low price
What sustained the Wii U, Mario 2D, and Zelda 2002 in HD? Besides the brand, the games need to have an impact. Virtua Fighter 6 has the potential to be an initial system seller until Persona 6 and Sonic are released, you know.
I understand your point, but you underestimate the potential of Sega's IPs. Almost 8 million for Persona it's a huge number, 4.5 million for Sonic Frontiers best selling Sonic in Japan , and 3 million for Total War are significant numbers.