There's actually no factual basis to that statement at all. I posted awhile back, that outside the young QB's drafted last year and thrown into the fire, a very low % of rookies played over 20% of snaps last year. And Paris was one of them.
After 3 games????? The Cards are getting play from Marvin, will from Robinson, Melton, Benson and the TE. That may say something about the Cards talent level but it's also pretty good. If a team can get 4-5 contributors from every draft class, they're going to be good.
These are 20-22 year old kids coming against adults with years of NFL strength training, playing experience, film study, etc. It's going to take a while for them to adjust and be NFL players. Sure, the new guys might have more natural talent, but it takes time and there are the exceptions but, for the most part, rookies are going to struggle.
People are on Benson but there is only 1 rookie RB, the kid from TB, that has done anything at all. Look at last year's rookie RBs. Bijan struggled and Gibbs was not much until the 2nd half of the season. And they were top 10 picks.
There are 3 former NFL players at my golf club(one played for the Cards) and I talk to them all the time. It's hard for rookies. They're in a new city, outside of the regimented control of college programs, learning a new system, some awash in money, trying to meet new people and have a social life, and so on. Throw in the fact that you're competing with older men trying to keep their jobs and support a family in a highly competitive industry, It's just tough.