Unfortunately, only by Wikipedia and Sierra Club definition. By law, the United States holds title to the land without any encumbrances or conditions of trust. This was originally done to facilitate disposal of the land by sale or grant which was the policy of the United States until 1976. In 1976, the Congress passed the Federal Land Policy and Management Act which changed that policy to retention and granted management powers to the BLM, NPS, and Forest Service to manage for “multi use”. The Sierra Club and others have invented the “held in trust” meme in order to leverage the FLPMA to kick ranchers, foresters, campsites, and marinas off of public lands.
You raise many valid points. However, the Sierra Club did not originate the idea of public land being held in trust by the government, that was original to the foundation of the country. I had a Constitutional Law class many, many years ago where that specific topic was dealt with at length in discussion of the Tenth Amendment.
I cited a Wiki link because it was quick and easily accessible, kind of like you cited a BLM link (was that you who did that?).