The Lockjack is a good idea for MRS, the rope has to attach to the device to activate it, or a rope wrench device is needed.
The Sulu Go works similar, but on a single rope, stays open until loaded, it rotates closing the two rails, or sleds.
https://hownot2.com/products/sulu-go
Another that...
Just a free running sheave on the Cric.
The tab on the spacer of the Ring Open would need to break before it could spin, but one of their rubber stoppers slide over it would keep it isolated.
Overhand on a bight below the friction hitch was used mostly back in the day, with a carabiner in the loop.
Low friction ring could go in the Butterfly, or a ready made Secret Weapon is the Cric.
Another splicing method might be a Tuck Bury, I’m going to send this one for testing, hopefully get as good of results as the Class II ropes.
The black rope is Teufelberger’s Rescue Assault, parallel strands with an inner cover of aramid, is the next challenge.
Courant’s low profile splice doesn’t have any of the core strands going through the eye, Teufelberger’s Drenaline SPlife has a quarter of them. A longer cover tail bury is suppose to make up for the decrease in diameter, but apparently the stitching plays a bigger part than other splices.
There...
Another ring option
https://hownot2.com/products/leash-ring?pr_prod_strat=jac&pr_rec_id=3fdc28a56&pr_rec_pid=8850950521147&pr_ref_pid=9632758464827&pr_seq=uniform
That rebraid method loses 40% of its strength, doing the math, a loop would have about 120% of the cords strength. One done with Tuck-Buries would be 178%, and certain soft shackles have a little over 200%.
The locked brummel can be done externally, instead of being inline, with the tails being...
The eye on a soft shackle isn’t a locked brummel.
Passing the tail back and forth a few time through itself doesn’t add much friction, with no locking.
Tuck- Bury has a fid and a half bury, locked brummels with the same length has a strength loss of 40%, the Tuck-Bury only has 1 1/2%.
The only way to do the second locked brummel for a loop is to unbraid and rebraid the tail.