You can not say IRS rules are more important than State case law for purposes of classification or this discussion. Such a statement shows the law is anything but clear. Federal/State classifications are an independent determination and require separate analysis.
Example, say A hires B as an Independent Contractor, having focused on complying with only the Federal factors, then B sues A at the State level after being was injured on the job claiming A misidentified B, whereas B claims he was really an employee and should receive workers comp. The Court is not going to apply the Federal Rules/Law they will apply the State Law, in fact we can go ahead and assume B was correctly a Independent Contractor at the Federal Level, but the Court could find under State Law B was classified and the relationship was that of employee/employer now A is liable for failing to comply with State Law and have to pay B's workers comp. This is the exact type of lawsuit that could be replicated hundreds or thousands of times sinking any Start-up, who fails to comply with any aspect of the classification paradigm.
>I am not a lawyer, but I am something like 99.999% sure that 1099'ing an LLC does very little to ensure that a contractor can't be retroactively classified as an FTE for whom W2 withholding was required.
As I said you are correct, just because you pay a company rather than a individual does not automatically make that an Independent Contractor relationship, but it is one factor. For example, in the Florida Worker's Compensation Statute (which provides its own factors, separate from both Florida Case Law and the IRS 20 Factors) factor number 2 reads:
"(II) The independent contractor holds or has applied for a federal employer identification number..."
[1] http://www.leg.state.fl.us/Statutes/index.cfm?App_mode=Displ...