Aikido pins are fairly easy to get out of, if you have someone's left arm pinned to the mat with ikkyo they can switch their hips by swinging their right leg underneath their left and sit through and you will in their guard. Having the arm is not enough to control them. That is if they know what they are doing, for the majority of situations it would probably be sufficient.
My choices for control would would be Kami Shiho Gatame and Kesa Gatame from Judo where you lock your opponents neck and spine to the mat. These work even on seasoned grapplers, the average person would have virtually no chance to escape if it was applied by someone with experience.
I would only use submissions in a very very serious situation where I had to immobilize someone quickly due to weapons or multiple attackers. It could be seen as a disproportionate use of force to choke someone unconscious or snap their arms.
So you suggest simply introduce a techniques from judo to fill up, what you perceive as a gaps in aikido pins? We all know that O sensei was well aware about judo repertoire of techniques having some visits in Kodokan. Being a Budo genius, he would also clearly perceive gaps in aikido pins. How come he didn't introduce more efficient pinning techniques from judo to replace those deficient from Daito ryu?
May be ultimate efficiency of aikido pins was not his main goal?