Does this mean that if I choose a base of 1 and use voice that my DEO will blast 11 Might at voice range as a level 3 spell?
Yes. At level 15 up, the guideline means Demon's Eternal Oblivion cast at voice range, the spell level equals the amount of might stripped, but below level 15 you get a boost because of the way the guidelines work. You see a lot of this with very low-level spells, it's what makes spontaneous spells so powerful.
No, the guideline was inconsistently written with regard to other guidelines, ignoring the issue of really low guidelines. The guideline has since been corrected. Look at the guideline it uses (see the errata). If you use a base of 1, it reduces Might Score by 3.
Edit: The spell is fine as written, as it matches the corrected guideline. Just don't set the spell's level below 3 unless you like guidelines less than 1, which can result in some real problems in my opinion.