I have never had an Eagle project rejected for approval. I have had them questioned once or twice.
My boys do a lot of "preliminary" Eagle projects throughout their scouting career getting ready for the "big show". They seek out, develop a plan and run service projects all the time. The older they get the more they "put it down on paper" and review it with an AAR with the other scouts. Sometimes they invite my thoughts on it.
As a result there has never been any need for an Eagle advisor, mentor, helicopter parents, etc. From start to finish they just do their project. I "glance" over their application for approval write up, but rely more on their explanation of what they want to do. If their spelling or grammar is not up to par? -- not my problem, not my project. If they are missing required items in the write up? -- not my problem, not my project.
All in all, I have enjoyed working on the Eagle projects, but then again, I do like being outdoors getting my hands dirty.
As far as the leadership part of the process, the Eagle project is often viewed as "outside the realm" of Scouting because it often incorporates non-scout personnel and it benefits a non-scout organization. The troop tags along because most of these projects are really a lot of fun.