Let me rephrase, as you yourself note. Professional genealogists don’t DEPEND on documentation from the LSD to certify lineage. For instance, last I heard it’s not accepted by groups like the DAR/SAR where a direct line has to be established to a participant in the American Revolution.
You are correct.
However, the LDS collection includes many millions of indexed records obtained directly from states, counties, government agencies and church registers. Usually the scanned source document is accessible. These are reliable, and very inconvenient to get from the original issuer otherwise.
The inaccuracies occur when John Doe submits a family tree he created based on the memory of his 90-year old great-aunt.