This isn't true at all with the current aero concept on these cars. The keys are the front wing, underbody venturi and rear diffuser.
The reason cars can't follow behind is not because of "turbulence". The vortices leaving the rear of the car are going up and over the car behind. The key to the second car's ability to follow closely is not that turbulence but the fact that the flow is directed up and over it - the updraft.
The updraft off the wings is one of the more crucial components of the total downforce. Lookie here:
As you can see, the air off the rear is directed upwards. Being that wings create downdrafts by nature, and racecars simply turn them upside down to create updrafts, it's pretty clear why the cars behind are unable to follow closely.
Here's a wing from an FSAE car:
The rear diffuser is a key player in this updraft. The rear diffuser doesn't directly make any downforce. The underbody venturi does. The diffuser simply serves to slow the airflow which was sped up under the car back down to nominal velocity. It does create a small updraft however, which contributes slightly to downforce, though that is not its purpose. But the interaction between the rear wing and the diffuser is very important. If the rear wing is close enough to the diffuser (within about two feet as I've seen tested in the wind tunnel on my FSAE car) then the strong updraft off the rear wing (note how strong that FSAE wing's updraft is) will act on the airflow exiting the diffuser, drawing it upwards as well. Stronger updraft = more downforce = more air being directed up and over the front wing/underbody venturi/body of the car behind.
There are two problems here. First, updraft is a big player in total downforce, so to enchance downforce a key point is to enhance the updraft. At the rear of the car, that means making the rear wing and diffuser work together. To do that, you put them closer together. Interesting point, given the new lower wings next year...
The second problem is that front wings are low to the ground. Why? Because of ground effect. A low, deep front wing will utilize ground effect - basically creating a venturi underneath it by squeezing and speeding up flow between it and the ground - to create tons of downforce with relatively little drag penalty. Ground effect is key - it's the entire reason an underbody venturi works, and it's why that underbody is so vastly important and actually creates a large portion of a race car's total downforce, all with little drag penalty.
Front wing ground effect:
Check this out:
It's an older Indy car in the oval configuration. Ever watched and oval Indy race? They can follow each other closely. Why? Because they have low-downforce aero designs, with high front wings, tiny rear diffusers, low AOA rear wings, and very little updraft off the rear. They can follow each other very closely, even around the relatively flat Indianapolis corners, and don't have many front grip issues until they get within about a couple car lengths of each other - at 220 mph. Formula-style cars don't operate like that:
You can clearly see a much stronger updraft off the rear of the car, high enough that the densest airflow will go right up and over the entire second car, 10+ car lengths back, easy. The updraft off my FSAE car is 10 car lengths long and that's only at 60 mph. Combine that strong updraft with low, ground-effect front wings and you get a recipe for cars not being able to follow each other closely around anything but the slowest corners.
So how to the new regulations play into this? Well, overall the cars will have a lot more downforce. The front wings are even wider and deeper, utilizing ground effect more strongly. The car's themselves will be longer, utilizing the underbody venturi more, enhancing the updraft off the rear diffuser. The rear wing is lower, closer to the diffuser, which will help to enhance the updraft coming off both of them.
I expect the following and passing situation to be even worse in 2017 than they are now. The simple fact is that the cars are gaining a ton of downforce. Do do that, you have to use techniques which not only ruin following for the second car, but also ruin your own ability to follow a car in front of you. These cars are designed to create downforce by forcing air underneath them, not preventing airflow underneath them like a NASCAR. And this philosophy simply does not work when cars are packed together. They're designed to work best in open air, plain and simple.
It is most definitely a fact that increased downforce is the direct cause of cars not being able to follow each other closely.