Support letters are important to an EB-1A petition! However, they are strongest when supported by objective evidence. If a letter says the client made "original contributions of major significance," that statement alone is not enough. Documentation is necessary to substantiate the letter. Think beyond the wording of the letter: do you have citations, implementation records, media coverage, adoption data, patents, contracts, metrics, or other third-party documentation?
TLDR - Support letters should reinforce the evidence, not carry the case by themselves.
This tip comes from an Immigration Attorney