IMO, the best way to keep people on a trail, is to make a trail that people want to ride, but in many cases peoples levels vary and this gets harder to manage. It is not a matter of who should ride it. I am a fan A and B lines. Let evryone have a shot at a good ride.
Lining the trails with rocks, sticks and dirt is not the best way to keep people on a trail. Aligning the trails across the fall line and bench cutting is ideal because it allows the water to sheet off the trail, and it is not easily altered by riders and rogue builders. 80% of trail widening and erosion is caused by poor alignment, not poor riders or poor construction.
What was observed 20 years ago is irrelevant, as 20 years ago, only now outdated hiker trail builder information was available to mountain bikers. Today many new proven guidelines have been compiled and presented in books from IMBA to make things easier for mountain bikers to manage. If you have any interest in building trails, not only should you read these books, they should be studied until these guidelines are always in the front of your brain.
Most rogue builders, do not follow updated guidelines or have access to labor and tools. They are easily discouraged when trails go to crap, and have no commitment to the park to encourage them to continue. The trails are generally not maintained and left to fall into disrepair or in this case get altered by new rogue builders.
Let me ask the public: Is it worth Jorba's time to bring this trail back to standards and risk a constant pissing match of vandalism, or should we leave it? You do not have to ride it if you do not like it.
Personally, I love the mountain bike experience too much to let this trail ruin my ride. I just ride elsewhere.
Enjoy your ride and have a happy 4th!