I don't know why that didn't work. You do have them all in the same file, yes? I know it seems obvious, but someone else failed to do that. Another obvious thing would be to check if you included acf_parallels_for_look_slope in the animations.py.
Beyond that, I'm not sure. Here's a more detailed explanation of how it worked for me.
Basically, I extracted all the native one handed combat animations from anim_human so I had a new animation file of 940 frames. Because you need a T reference pose (all bones 0/0/0 rotation) at frame 1, I added an extra hundred frames, so the actual animations started at frame 100. That was just so each animation sequence began with a number ending in 0. I exported the whole 1040 frame animation as an .smd and imported it into a new .brf file in openbrf, calling it onehanded_attacks_roundshield. I referenced only the default middle height animation as you have, so for example;
["ready_thrust_onehanded", acf_thrust|acf_parallels_for_look_slope|acf_anim_length(100)|acf_rotate_body|acf_enforce_rightside,
[ready_durn, "onehanded_attacks_roundshield", 200, 210, blend_in_ready],
["release_thrust_onehanded", acf_thrust|acf_parallels_for_look_slope|acf_anim_length(100)|acf_rotate_body|acf_enforce_rightside,
[0.61, "onehanded_attacks_roundshield", 210, 240, blend_in_release],
... and so on and so forth. It works fine for me.