Most failed cases of I-140 application were attributed to the poor writing or ill-conceiving of the cover letter. In my opinion, here we need to teach an immigration officer probably only with high-school education the research we have been doing and convince him that we are excellent in plain and flawless language. It took me 9 months to write and modify the cover letter. I had fewer and less prestigious publications, the recommendation letters I had were mostly from assistant and associate professors, but I succeeded in EB1a without any hassle.
I simply don’t trust the blood-sucking immigration lawyers. They are the most incompetent among their peers in law school; the bright and smart ones have gone for better paid and more respectful jobs. If you could first-author research paper on a good journal, you can do it yourself.