I understand your frustration with such discussions but I think the approach you're taking in your response is flawed.
1. In cases where Aikido seems to be vulnerable to other arts strategies, to simply say it's because no one really undertands aikido well enough to make it work in such circumstances is of limited use. I mean if someone who's been doing it 10 or 20 years hasn't learned enough to defend against someone who has been training in another art for 2 years, it really doesn't matter if that's because aikido is missing something or because the practioners haven't found it yet. Functionally it amounts to the same thing.
2. The "oh but a Master would have been able to..." approach is similarly flawed. No one will take this arguement seriously until there's evidence of a "master" doing what you claim. This is the sort of response that is actually lampooned by the types of people who start these discussions (along with the too deadly to spar argument)
3. It's a huge mistake to assume that eveyone who thinks Aikido is lacking in some areas compared to other arts is
a MMAist who practices Aikido a little to "work on his locks," or whatever, and considers him/herself "knowledgeable" about the art
There are people who have been studying Aikido for fairly good lengths of time, in depth, who are happy to admit Aikido's limitations. This is as it should be - as discussed in the "False Confidence" thread.
There are better ways to head off these discussions. For example, I have no doubt that on the whole most aikidoka would be beaten by most bjjers in a one on one engagement. There's no need to get into a discussion of which aikido techniques could be used to defeat the bjj'er if only people understood them properly. The more effective and accurate response is - "so what". And this is the point, art vs art discussions are silly because they are talking about an artifical "what if" that is never likely to happen, and is not what we're training for.
"Aikido vs..." discussions can be usefull exercises and help us to examine our art and get a more realistic view of both it's strengths and weaknesses. But I think you're right in that oftentimes people that start them, do so with the intent to criticise Aikido. Which is silly. It's like saying a 4x4 is a crap vehicle because a ferrari will beat it in a time trial. Same thing here. BJJers can take aikidoka down and aikido doesn't have a good defence to a back mount with hooks in? Ok interesting, but that's not what Aikido was designed to deal with so it's no big.