please, let's not get into that whole argument.
our rationale for increasing Imix's power level: RttToEE preceeded the BoVD, and if i'm not mistaken, the ELH as well. so, when Monte was writing that module, he had no other unique planar entities to compare to. working from a 2E perspective on power levels, an Imix of CR under 20 sounded perfectly OK.
then came the eventual power creep of 3E, which brought the power levels to all new highs.
having stats from the BoVD, BoED, and Demonomicon articles, we decided that having an Imix who was that weak by comparison just wouldn't work. do we keep the other archomentals around a similar level to make them match? do we put them where we want but keep Imix weaker? in the end, we decided to stat Imix how we wanted, and call his stats from the module a "lesser aspect".
now, if you like the demon lord stats from FC1 rather than the ones from Demonomicon then you probably also prefer the RttToEE Imix. it shouldn't be a great challenge to knock some HD off the other archomentals and have them at a similar power level.
if you disagree with what we did, well - it is a free county.
that's all i have to say about power levels for the article.