We have wrestlers, jujutsuka and karateka in our dojo. Sometimes it gets out of hand
My experience has been that the modern finishing position of ikkyo and the transition from the second to final pinning position of nikyo omote are problematic.
OTOH, I've found the intermedate pinning position of ikkyo and nikyo to be very
effective in pinning them.
The "intermediate position" is as follows:
o Your inside knee down but your outside knee up.
o Your inside foot should be up on the toes (i.e., keiza not seiza), your outside foot should be flat on the sole.
o Your outside shin should be vertical and your outside thigh parallel to the mat.
o Your overall position should be turned a little toward uke.
o Keep your inside hand firmly grasped around uke's elbow and your outside hand around the back of their hand (for the x-dori and tsuki attacks) or wrist (the x-uchi attacks).
In that position, rather than go on down to the finished ikkyo position, stay up and use uke's arm as a spear, plunging it into the mat. The more vertical, the better.
Uke, even very flexible ones, have trouble getting out of this pin. For the folks not on the "Left Coast" there is, of course, also the threat of breaking their elbow.
There are also possibilities of nage pinning uke's arm in the fold of his thigh and having both hands free to apply handcuffs or whatever.
If you can get a copy of The Founder's book "Budo" or Aikido Journal's remake with Morihiro Saito Sensei, you'll see some of the positions I'm speaking of and the older, more effective version of the ikkyo pin.