Well my opinion is that everyone should have relatively have similar tunes, because the game wants you to drift 1 type of way. and to drift that type of way everyone would need similar tunes, All depending on there style, but what i'm really saying is we should all be using the same formula for everything but spring rates, because that's what creates your Style
I don't know where you're getting this from at all. In my opinion, that statement is completely false.
I can easily say that whether a person uses the D-pad or analog stick for steering will change both the approach to drifting, and tuning outcome.
That same difference gets even more exaggerated if you look at wheel users, which encompasses a wide variety of wheel setups. Everything from T500, to G27 & G25, even DFGT.
All of these wheels have force feedback options, which are different from person to person based on preference.
Some people use a full 900' of wheel rotation, while others use as little as 180'.
Some people have a handbrake mod, while others don't.
All of these factors can and do creat major differences in how a person likes to tune their cars in order to get the desired response from it.
And to be really honest, that's just the tip of the iceberg when it comes to the list of things which can cause a tune to be different from one person to the next.
Then there's each individual's approach to drifting. Drifting is 100% a subjective endeavour. No two people share the exact same view on it.
-how a person likes to innitiate has an effect on the tune. Same with how they like to transition.
-whether a car is setup for doing short, competition style sections or whether it's set up for running full laps of certain track has an effect on the tune.
-tunes vary from track to track. A car setup for doing full laps of the 'Ring is going to be different than a car setup to run full laps on A-Ring Mini. Back when GTP FD was still running (this goes back to GT5 actually), a couple of the guys on my team who were very successful were building custom tunes for each specific round of the championship. They were changing the HP, torque, amount of limiter, transmission, diff, ballast, and most definitely the suspension between each round. The "Madrid tune" looked a lot different than the "Fuji tune".
I could go on for days listing reasons why tunes would be different from one another. Overall skill level is another huge factor. I know guys who have certain cars tuned up so tightly that, should they take a break from GT for a significant time, they won't use those cars until they're "back in the groove", which can take the better part of a month depending on playing time.
With all that said though, there is actually a magic formula for tuning that most of us follow.
We spent time learning to understand the subtleties of tuning, and how each variable changes a car's performance. We then use that understanding to build a car which suites our wants and needs, so that we can achieve the desired outcome.
I'm not trying to be sarcastic or anything either. That really is the formula.