That rather depends on the type of park. Its far more of a challenge stalking a specific animal out of a large herd and in an area with very little cover below 2m due to browse line than it could be stalking Roe buck in the wild which can be far from a challenging stalk! The actual stalk/approach of the deer is only a very small part of the Level 2...
I have done both park and more often wild.
If you know the park well, you will know your limits and boundaries, and with Fallow depending on the time of year they can be difficult at times in a park situation. Due in many ways to the fact that you have so many in front of you and picking out the right beast, with a safe back stop is not always as easy as one might think.
However you know they are within the confines of a fenced or walled area and therefore you will see deer and there is to my mind a high chance of your securing a beast. And if the stalk onto the beast fails, it will not be long before your back onto another beast. Yes parks have to be big enough for the deer to run away, and many are, but would you say that a 200 acre park is enough for the deer to run wild?
In a wild situation if your stalk fails it is most unlikely you will come onto the animal again. There are variables with both aspects of park and wild, but in my opinion it is not the same as stalking in the wild. How anyone can compare stalking, lets say a park Red Stag, to a wild Red on a Scottish hill side is beyond me. The extraction alone is going to be a lot different off a hillside compared to a park!
To me, and again its my opinion, it is a world apart. I know many mention you only have to prove you can shoot and gralloch 3 deer, and its all the same. But killing 3 deer in a park situation is not comparable to my mind to taking a deer in a wild free range situation.