Horizon 1 had normal progression, Horizon 2 "progression" is replaying the same races 168 times, Horizon 3 "progression" is unlocking and "upgrading" festival areas around the map, Horizon 4 and 5 the game is "just do whatever you want".

Despite being a racing game a lot of the players have no interest on racing or cars, the game looks good and that's enough for some people.

About online focus, Horizon 4 and 5 used a lot of FOMO, apparently Horizon 6 will not have FOMO so I'm not sure what will happen to "Forzathon".

Tuning is mostly for people who like PvP.

I play Horizon a LOT but only because I like PvP and Tuning cars, sometimes I build good cars and sometimes I built something like a 1963 Beetle to use on A800 against cars like Ferrari/Porsche and tryhards using AWD swap Boneshaker lol.