It's easy to look at an eval as a pretty simple thing, from the outside it just looks like someone answering questions, right? But a lot of times it can actually be pretty stressful for the person being evaluated. It's not really just a matter of giving a report and answering some mundane questions from a few people (although that certainly is part of it), it's about standing up on a pedestal in front of everyone and asking them to judge all that you are. And sometimes OD has been known to judge harshly. There is an anxiety involved in waiting to find out if you measure up to the standards of the populace, and that's not even accounting for the fact that evals have sometimes been used for particularly disgruntled members to unload their criticisms with impunity. Not all members up for eval need to deal with that thankfully, but some do, and even for those that don't, it can be an ordeal nonetheless.
As a vetting process it works pretty good. It's a bit easier to endure if the opportunity for a promotion can come at the end of it, and it serves as a pretty good discouraging punishment for those who might otherwise tend to slack on their responsibilities, but it's not exactly something I would subject someone to just for giving routine reports. I suspect in some cases it may even be one of the reasons some members don't ambitiously try to vie for the higher General ranks more, in their mind it just isn't worth the hassle. But I won't say that definitively as I can't say for certain, never asked them myself.
In any case, rather than having Generals or in this case Commanders report to you on their performance every 6 months, maybe you should just ask them what they have been doing lately? Maybe ask their peers? I'm sure a lot of the Generals, and fellow Commanders, can shed some light on a bit of our recent activities. It's not like we've been trying to keep it secret, we just don't make a habit of parading our accomplishments around on a daily basis.