I'll agree with most of your points. The FM5 physics engine is great, as is the graphics and sound. The issue is the things that build upon that to make a Forza game were missing or half finished. You can't share paints and tunes and race your mates like you could in previous titles. No car clubs. There's a maximum of 10 replays. Period. All your old peripherals - like the £300 wheels MS launched in partnership with Fanatic 12 months previously weren't supported. Own goal after own goal, and T10 just stuck their collective heads in the sand and avoided providing any answers pre launch.
Credit where it's due - T10 added some things back in like drag racing and the no-cost track DLC, but it was too little too late once the trust had gone come the glorious Xbox one launch.
I'll quibble with you about the tracks - not recycled. T10 binned all the existing tracks from the 360, laser scanned them all and recreated them from scratch. The old 360 versions were knocked up from GPS data IIRC. The feel of places like Road Atlanta and Laguna Seca are very different on FM5. Which is a good thing. Just took them a while.
The community has just died in the last 12 months. A topical example - Virtual Motorsports is closing down as of today. They were getting an entry of 140+ people for the classics series in FM4. FM5 numbers were 20-25 on a good week. What's the point, when someone has to devote their own time and money to running a site for their hobby, and they don't really like the game it's there to promote?