Yes. The vast majority of non-privileged entities blindly outsource payments through companies that make those presumptions - whether based on Agency fear, and/or because they directly benefit from the confusion.
Funnily enough, this is very close to my situation. But I have had trouble in the past with Correcting 1099s (via LH/CtC, which has its merits, but certainly its flaws). Would you be kind enough to go into more detail of the structure of your rebuttal? Are you also sending a Corrected 1099, referring to LM, or are you adding it to your 1040 and calculating an LM Deduction?