I guess when you're talking cars among the two franchises, Gran Turismo has been more about a collective appreciation of automobiles (say what you want about cars chosen for GT titles) while Forza has been more appreciative of what most gamers would want to drive and race in a game.
Both cars and tracks are the most important elements of any racing game. How you establish a connection and a bond between the two defines you as a racing game and as a franchise. Messing up this bond drastically compounds your game. There's a reason these two are at least among the best sim-oriented racing games on consoles. Both have good numbers of cars and tracks as well as quality among the cars and tracks along with decent usage of both. There are certainly more venues I'd love to see in GT games, and I do think Forza may need to try some more different locations and venues to expand their lineup of courses just a bit more. GT can use a bit more diversity among cars even though the car count is usually high. I can't complain too much on what Forza needs on the car front, though.
I agree with everything you said there. On another note, I feel neither do an outstanding job when it comes to gameplay. There's no innovation in gameplay at all with GT5, and indeed some fun content like the driving missions were omitted. But night/day racing and 3D are handled very well indeed. I feel PD pushed the genre on in that single respect. On the other hand there seems to be a bit more variety with FM4 as choosing a particular car and then entering a race it is fit to compete in. In GT the player is pretty much expected to know which of his cars is competitive for a given race. That's an outdated approach to things.
As for track/car combos, neither of the franchises does it for me. My personal favourites were Grid and the Shift series, but these franchises have a totally different focus. I fell out of love with any of the original tracks in both franchises and while I know it's extremely expensive and time consuming to create tracks, there are so many real life tracks worth taking a look at. I'd just wish there were a track creator more powerful. In any console game besides ModNationRacer.
I guess I'm sort of confused as to what you mean by this section. Are you basically saying that the physics are better for stock cars in GT5 or...?
To me, driving stock cars is a lot more rewarding in GT than FM - that's what I was trying to say.
As for tuning and setups...
An interesting way of looking at the difference to the two and not one I had every considered.
Personally I treat cars in both titles pretty much the same way, in that I will either leave a car totally stock never intending to modify it at all (The Quattroporte in FM4 and McLaren F1 in both for example) or I will own two versions of it one modified to a certain class and one totally stock.
Not something I've even done consciously its just happened in both titles.
One question, when you say "I'm still not convinced T10 has tackled the problem of glitching the physics engine through tunes. " are you referring to tuning as in parts or as in changing settings?
Scaff
I used to run at least two different version of every car in each class, built to spec and setup either for grip or speed. So a build and tune for Mugello should do well on Silverstone as well. Sebring and Nordschleife were often a good match, as were Maple Valley and Laguna Seca.
On AWD and FWD cars the very first step of tuning used to be setting the ARBs at 1/40 and not changing them throughout the tuning process. That's one example of what I refer to as "glitching" in FM. As I have a feeling neither franchise has reinvented its physics model, I'd be very much interested if this is still possible in FM4. I know T10 tried to address some issues in FM3 by penalising a car bottoming out by invalidating the lap time, but that's surely no cure for the underlying problem: people running far too high rebound settings for the stiffness of the suspension. One way of finding this out, finding out if the physics engine is coping with unusual setups, would be looking at the tunes themselves. But since they are locked/lockable since FM3, there's little way of doing so. To my experience there was on tuner garage which built competitive driver's cars, and that was Slopoke in the FM2/3 days. I believe Dust2Death is still around, but I really couldn't say.
So what's with GT5? It's amazing an engine with so few user changeable variables still gets thrown off track from a simple ride hight glitch. The whole power limiter/ballast options get abused. Yet, there's not much to fiddle about in the first place. A bad thing? Depends entirely what sort of gameplay one is after.
I feel if comparing both FM and GT you can't compare an apple with an apple because the key elements are so different. FM is about taking it online. Once you are there you'll find some very fierce competition. To keep up one could try tuning a car by oneself or try to find a capable car on the AH. How close the latter is to real life, how robust the physics engine is, one can't simply tell because most likely the tune is locked. But you get rewarded with the most comprehensive leaderbord ecosystems out there. What gets left behind in my view is the sensation GT gives me.
The online part isn't hardly worth bothering in my opinion. In turn there's little need for me to fiddle with car setups/upgrades on street cars. The Time Trials are also lacking quite badly in comparison and hold little motivation.
So what's basically left is the most comprehensive Miata and Skyline collection on earth. And that's where the fun starts, really. A-spec is a very tricky beast to stage a good race. It's more like an endless Best Motoring style 5 laps battle. Arcade is still a bit rough round the edges. For example to give the AI a bit of a head start I usually chose a softer tyre compound at race start, which the AI then uses too. Before the race I switch to a harder compound myself and voila, I really have to fight for the win. In an race which I try to stretch to about 1 hour. There is no need at all to alter the characteristics of any stock car at all when playing the game this way. The physics engine works pretty good in these circumstances, and rather worrying about camber settings or caster or spring rats, 100% of my attention is devoted to the driving. In order to save the tyres to make my pit strategy work. Throw in some damage and the race really gets exciting.
To conclude this, FM never gave me this particular enjoyment. It was good fun hanging out with the guys, and I happily say it again GT can't compete in the online side of things. But up till this day (with my very limited experience of playtime in both FM3 and 4) GT provides the most authentic and believable sensation of driving an actual car of this make or another because that's what it does best: take a thousand cars and take them to a track. FM on the other hand lets you do a thousand things to any one car. Which, in the end, doesn't make me care for any of the cars in the end. The choice of car becomes totally random.
I wished both GT and Forza should be (re)viewed in their individual natural habitat. That would be fair in the respect that each developer put their best effort in them.