And I think that the point, it is not that BJJ, any ground fighting or aikido is crap or even complementary. I think it is more that they may not be worth ones while given the particular society/environment it need to be considered into.
I can not find the post or the poster but after reading his post, an in his context, It does make sense in some modern police forces to use the guard position.
On the same token, we need to note that the medieval and 16-17th century hand-to-hand ground wrestling that both fighter going to the is almost totally absent. (Other than what seems to be "untutored" wrestling, young man play and judical dual in full plate.)
There are plays to defend against shooting high and low. It is limited to the entry/initial grab phase. (it is the same for all the grabbing methods but the low and high shot are mentioned specifically). and there are pin where the oppoenet is on the ground
This tend to indicated two things, that it was something that you could face hence it was done by some people, and that going any further on the ground may not have been an option considered viable at the time. It does not mean that ground fighting is pants; it was just not relevant given the circumstances.
On the same token, A German 15th century open hand masters seems to believe that "spiting and biting" was at least a nice get out of jail free card.
The eyes, the lower maxilla/mouth ligaments, the temples, the neck the throat and along the collarbone, the solar plexus, the navel, the goolies and the knee are designated as targets for pressure and strikes. (or under the arms pit).
As one poster said it does not help so much when on the ground but it sure does help you to go there in the first place. So in this context, it is valid.
If we have a look at that picture http://www.thearma.org/Manuals/Goliath/187.jpg
(the text is from the 15th ,The illustration from early 16th)
I would transcribe the text like so
Greifft dir einer vorn bey dem goller, So grief im mitt deims linken vornen in das glench und reiss im umb unt setz im demen recht arm auf sein linken arm aussen auf sin elbogen glench un stoss indes zur erden (so.y.im.d an) und drit im aus dem stos auf dein recht und nimt des stichts mitt der rechten.?. domit du im im .e y stosst
Roughly translated that means,
An arm breaker
Should one grap you by the collar, at that time grab him with your left in front in the arcticulation and drive (that) him around and set your right arm onto is left arm onto the articulation of the elbow. And at the same time "enter and press (with that last bit)"towards the earth and press him with the irimi onto your right and grab the thrust with the right, with that you ??something?? "enter and press" at him)
Stopping the wrist one way, pushing the elbow the other that does have a nikkio flavour, I can see why it make sense at the time bollocks dagger are usually bigger than modern knife and you wore several layer or tightly woven fabric. So the risk of being cut is relatively low, now it is a little iffier to try that in a T-shirt with a modern knife.
To go back to our the topic, in the medieval context they have chosen for what ever reason, that going to the ground was a bad idea, so they have developed application of principles that will prevent it to happen. The very same move is used against unarmed opponents.
I can see the same concept applying to BJJ alone and aikido alone, so you do not necessarily need to mix the two, nor it is evil to do so. I think there is valid reason to go either way.
That being said, if you chose a stand alone way, seeing those application once and while could only help.