For me, the DS3 was foreign to start with. I purchased the PS3 when GT5 came out. I could "get by" using the DS3, but it was anything but natural. I wasn't a gamer with years (or a literal lifetime) of experience using the DS3 and its predecessors, and the concept of driving a car using a joystick never felt terribly comfortable. I learned to make do, but that's about it. I haven't looked back and won't be using the DS3 again in a driving simulator. My experience using a game controller (ie a DS3 similar device for the PS2) to drive was limited to some 4-wheeler game a former girlfriend had, and which I played maybe a few dozen times in total.
I did, however, have about four decades of real driving behind my belt, along with some particularly good (albeit, odd in comparison to what others I've known had to accomplish) drivers' training my Dad forced me to go through prior to being allowed to take my license test, so the wheel was a far more natural transition, regardless of the limited feedback provided within the game (there is no real lateral acceleration, there is no real peripheral view, there is no real vibration, there are fake, forced, lighting affects and other forced and ever-changing discrepancies between the game's physics and real life used to increase "dramaifficulty", etc), or for that matter, the fundamental limitations of affordable wheel units to simulate reality.
If it took some people months to get used to a wheel over the DS3, I can only say that based on the gAmER phenom and the particularly naive and imo somewhat deluded culture it has created, where the line between real life and simulated or arcade experience is blurred, often beyond recognition, by those immersed in it, I"m not at all surprised. There are still those who occasionally claim that driving in this game using a DS3 is valid beyond the "game" aspect, which is simply isn't. That is, you won't be gaining a real driver's license from taking a virtual test using a DS3 anytime soon, TG.)
However, it didn't take months for me, and imo, it really shouldn't take anyone who has been driving a real car for more than a learner's permit or occasional driving "weeks" or "months" to become comfortable using a wheel controller. If it does and you have been driving for years, then I'd suggest you may need some remedial driving classes or you're jeopardizing the safety of yourself, those in other cars around you, and your loved one's lives.
In this game, and for me (can't speak for anyone else, but I suspect many would concur) most the "getting used to" was because the game is missing feedback I take for granted when driving (stated in-part above), and the wheel-unit (ie, wheel, brakes, shifting) itself isn't quite "real" either, leading to a need to adjust for the wheel unit's (wheel and foot pedals) oddities.
In any case, being comfortable doesn't mean you will ever rank in the top ten drivers. The reality is that some very few can, and most of us can't and never will. I don't mind stating that while I'm a good driver, and in real life, I've both avoided and gotten myself out of some pretty serious situations due to the training my dad forced me to complete prior to taking my license test nearly 40 years ago, along with perhaps a natural feel for the wheel, and I can drive as fast as any cars I've ever owned will literally allow, I'm not top ten and I never will be. it's ok. The idea is to drive well enough to enjoy oneself, get where you're going, and to avoid (to the limits of luck anyway) being injured, maimed or killed, and preventing the same condition from our occupants and drivers around us, all while not living a white-knuckle existence.
I'd like to close reminding others that being a good driver is no perfect shield either. My (former) car got whacked a few weeks ago when a driver sped through a red light and rammed into my driver's side rear quarter panel at ~35mph. Fortunately it was the wheel, rear axle, and quarter panel that took the brunt, (surreal experience...) rather than my door and MY left side, and a few thousand dollars later, I'm in replacement car instead of lying in a hospital bed. (TG other driver and her passenger weren't hurt either.)
For those of you who believe the DS3 is "the" thing, I'd suggest that if you can get a wheel, get one and give up the 6-axis and learn to drive, even if you're not as "fast" when not leaning on the fake gizmo to raise your supposed skills well beyond reality... even in a sim. It just teaches bad habits. And pay attention. Most accidents are caused by people not paying attention. Get off the f-ing phone, quit focusing on your chatty passenger who expects you maintain eye contact and to watch their every funny hand movement while talking, use your turn signals when changing lanes on the highway, and for God's sake, put down the gd blunt.
PS> IMO, if you ever need to rent a mid-sized SUV, don't choose the KIA Sorrento. It has lots of pseudo-luxurious crap, but for driving, it sucks rocks. Boaty suspension, overly sharp brakes, and the "blind spot" consists of almost the entire rear view.