I've tried that method and all the concerns are mostly well-founded. If you manually adjust it so that both "legs" of the eye take the load equally, then it's impossible to release under load. And yes, you do have to manually adjust it.
On the other hand, is there any way to put an eye on a horn cleat so that you can release it under load? By "load" I mean enough tension that you can't create any appreciable slack in the line by applying a force perpendicular to the line.
Basically, NO...that is why it is important to take the end of the line WITHOUT
the loop aboard your boat and cleat in the proper figure 8 manner.