As for my .2 cents on the Horizon formula, I'll be honest with you: what we have now works, however, it could absolutely take a turn for the better. I do not understand how, 15 years later, TDU still does things better than any other open world racing game. Car-specific HUD clusters, discoverable dealerships, houses with an actual purpose (Horizon is closing in on this, and The Crew kinda-sorta misses the ball here but is better than Horizon), and clothing.
Pretty much the same thing happened with the Forza Motorsport franchise though. A few titles in and they really stopped actually advancing things much outside some physics tweaks, graphics and updated car lists and it ended up feeling like lost potential as it grew really stagnant. Even FM7 doesn't offer some features that many PS2 racing games had.
People try to take the blame away from the devs and say it's the 2-year cycle to blame, but I dunno if that's really the case and feel like it's probably more down to complacency. We also don't know how much M$ guides them and tells them what to do, seeing as the Forza franchises are their babies.
While it's probably not as big of an issue in Horizon as it was/is with Motorsport, I feel like they are kinda stuck in the middle with their identity.
Horizon is kinda stuck between being a total arcade game that appeals to casuals and children with massive jumps and goofy dances and stuff, and being an open world version of Forza Motorsport for driving enthusiasts and car culture people. They have this silly music festival idea and always try to force you into hypercars and racing in S2 and AWD V12 swapping everything, meanwhile the smaller cars in lower classes get totally ignored even though they are better suited to clean racing on the roads. For every "British Racing Green" style thing they put in, they add in some Halo Warthog challenge or something. They add cult cars like the Hillman Imp that should be appealing to car enthusiasts but generally get ignored and instead they encourage you to drive Lamborghinis and Porsches and stuff the whole time.
I'm not suggesting they need to go one way or the other, just pointing it out more as an observation of the similarity in the arcs of the series.
I feel like Horizon hasn't gotten as bad as Motorsport on that front yet, but Horizon definitely has a lot of wasted potential by just not using the stuff it already has very well.
I think what they need is some actual competition. It's competitors are basically doing what PG is doing, just on a smaller and cheaper scale, quality wise.
Maybe it's just me, but I don't feel like there is a lot of competition going on in racing games right now in general. FM8 might change it based on the info coming out of the beta testing, but it hasn't felt like GT and FM have cared what the other was doing for years now. A lot titles feel like they just crutch on their name value and/or whatever their exclusive deal is with whatever series/manufacturer.
The sim market is probably the most crowded right now, but I don't feel like any of them care what the other is doing or are making any efforts to outdo each other.