This is FUD. For starters, how would he, as a Playground (ex-Playground now) person have access to Polyphony or SIE's GT revenue numbers? We also know that GT7 alone is at least around 10-12 million in sales, and has a healthy live-service component. It's not a GAAS per-se (as in, purely online-only), but we know from its sales it's sold more than Forza Horizon 5 (at least, pre-PS5 port).
Like bro, yes FH5 is a good game and it's done well, but this is the type of self-fellating reacharound flex I hate from MS and Xbox developers in general, even if they're ex-devs. They make claims that cannot be proven because it'd mean they have access to financial records of other IP and companies when, realistically, they wouldn't have that access. I can buy FH5 generating more revenue than, say, GT7 in its debut month on PS5; that's a perfectly reasonable take.
But lifetime? As in ALL entries combined? It's bullshit, and I don't expect an IGN-owned GameIndustry.biz lacking Dring to do any fact-checking on it. Not these days. Trying to make that claim for FH5 over other franchises like F1 and Need for Speed is also dubious at best; keep in mind some of those stretch back to 3DO/PS1 days and I'd never consider NFS to have been a niche franchise (it's also been multiplat its whole life).
Just another example of someone saying something frivolous and usual lapdogs & fans who don't have critical thinking, taking it at face value, before questioning the logic behind that statement. All because they're coming from supposed authority figures.
Sad, man.
EDIT: And if he's talking the entire Horizon franchise, my statement still stands, at least regarding GT. The first couple of Horizons weren't huge hits (they did well enough, tho) and each mainline GT's seemingly done at least 10 million units. There's also GT Sport, which sold quite well and had its own MTX revenue streams and, again, we have GT7 today.