It seems to me there are a number of factors that have led Kaz/PD astray.
1. The growth and misunderstanding of online updates and multiplayer
When I played GT1 back in the day there was no online. Games existed in a sort of vacuum, solitary confinement if you will, where they couldn't afford to be released with game breaking bugs because there was no way to update them. Glitches were always present, and would be well-documented and immortalized into the game's history but most things worked because developers took the time to bug test properly - they simply had to.
Today, in too many cases it's become common practice to shove games out the door without proper testing, in effect turning a full price game into an open beta. Online updates are great for fixing rare, hard to find bugs that make it through testing, or for introducing new features/content, but if they are going to be used for an open beta (which is basically what GT6 was at release and still is in many aspects) then we, the customers, should be told so ahead of time. The developer needs to make the effort to have some form of communication with us so we can give solid feedback and get game-breaking bugs fixed in a timely manner.
The other part of the online issue is multiplayer. Multiplayer is great, but too many developers are skimping or outright ignoring singleplayer in favor of it. I can understand why: it's far easier to release base content for multiplayer and let the fans (customers) make the storyline/structure and compete amongst themselves, rather than developing a compelling story (namely for a racing game, career development and proper racing/championships) and AI for singleplayer. GT6 singleplayer feels like it was meant as a trainer for online, and even at that it does a pretty poor job.
2. Bad timing
This one isn't all PD's fault. I think there was strong pressure from Sony to get GT6 out the door for Holiday 2013, which I can understand from Sony because with the PS4's release the PS3's days are clearly numbered. If GT6 had been delayed into 2014 then I think it would have been either moved to the PS4 or dual-released on both systems. In my mind, PD would have been better served to release GT6's cars/tracks and physics as GT5 "Ultimate" or several DLC's/feature updates strung out over time while working on GT6 as a brand new game purely for the PS4.
3. Kaz's Vision (or arrogance/stubbornness depending on your point of view)
There is no doubt in my mind that Kaz has huge dreams for GT. This is great, but I think it leads to trying to do too many things at once and missing the basics along the way. Basics that are lacking are AI, elements of racing (practice, qualifying, grouped starts - grids/rolling), and fixes for bugs that affect those things (eg AI wheelstands, pit stop bug). Meanwhile we are nearly 3 months into this game and are still facing gameplay bugs (though, to be fair, some have been fixed) while still waiting for features promised "shortly after release".
When it comes to constructive criticism of GT, it seems Kaz either is oblivious or purposely not listening. Case in point singleplayer, which has failed to evolve much from GT1 some 15 years and 2 systems ago. Likewise, sound and AI suffer from much the same condition. Perhaps it's a cultural thing, or perhaps Kaz views GT as a work of art, rather than a game, and therefore nothing is wrong with it (except bugs, of course). Perhaps he's trying to market a global game to his local country and doesn't care what anyone wants outside of Japan. Perhaps he refuses to look at what other developers have done and prefers to reinvent the wheel at every step. I do not live in Kaz's head so I can only speculate as to the cause, but we are all dealing with the effects.
The Solution?
Kaz can (and will) do whatever he wants and we'll see how that works out for the franchise. One thing that Kaz could decide to do literally right this instant that would go a long way to satisfy myself and, I suspect, many who feel similarly is to simply communicate with us. The medium is not nearly as important as the act.
I don't care if it's a weekly blog, Twitter posts, or a monthly "state of the game" update on the GT website, but do something. I don't care if it comes from Kaz directly or someone at PD so long as it is official and not just random leaks/propaganda. This is not rocket science, it's called customer relations and it's a useful tool for keeping customers informed and happy - generally a good goal for any business. There is no excuse for leaving your customers in the dark 3 months into a game's life wondering if basic bugs will be fixed and if old features will return, not to mention if they will ever see new features promised at release.
If February ends with no word from PD then I believe I will have given up all hope. I have no more breath to hold. At this point, I am basically approaching GT6 as an abandoned beta. Updates will be greatly welcomed but not expected. I will get as much as I can from GT6 and then look toward PCars as my next potential racer.
I've poked a lot of fun at the GT tagline "The real driving simulator" but in the end that seems to be where PD is focused: a great driving experience with little to no racing. It's quite unfortunate. Gran Turismo has so much potential.