I kind of agree but I'm leaning more towards the reg freeze. Most teams choose to work on the back of the cars and not the front in the off season, as they were not allowed to make structural change in both areas. So whatever inherit limits they had on the front last year, they're still there this year. Meaning that they've probably clawed back most of last years rear DF, all be it with a little more drag as they've had to use the rear wing a little more.
I would also add that they may never have clawed back all the front wing DF after the change to the front wing regs of a couple of years ago that forced simplification of the front wing and outlawed the double stacking...RBR racing's "hard to drive car" seemed to coincide with that reg change, which also opened the barge board area for development. They had seemed to find something late last year to make the car more stable.
The McLaren current car traits could probably be traced back to those same front wing/barge board reg changes.
All speculation of course...