Let me start by saying I only have a few games of TED played so far, so I certainly haven't personally experienced all the possible scenarios you mentioned. With that said, here are my thoughts:

I think there's certainly room for debate on what "Use abilities" exactly means, and there can be a spectrum of reasonable interpretations. But I believe the "On your turn" phrase is much more clear cut, so I would suggest limiting the scope of this round of potential changes to focusing on this criteria, and see what the downstream impact is.

I believe the Plains (Safeguard) ability is the only one from the regions that falls under this category, and implementation-wise, I suspect the programming logic for the Plains (Safeguard) could be essentially identical to the Desert (Mirage). If this were the only change you made, that could be a reasonable choice.

However, if you decide you want to consider "On your turn" regarding copying other Defenders' abilities, here are my thoughts (again I'm ignoring the active/passive issue for this ticket):

- Ezru Courage: Agreed that is your turn, therefore enable/disable it based on your active/passive decision.
- Laishom Command: My interpretation is that "As soon as your Defender card is drawn", it is already your turn, because the end of that ability says "...and then continue your turn", not "...and then start your turn". Therefore enable/disable it based on your active/passive decision.
- Lealith Retribution: Not your turn when you would defend, so would never apply
- Oryk Martyr: Not your turn when your teammate would defend, so would never apply
- Oryk Strong: Can be during your turn, Active/passive decision
- Um'Tak Berserk: During your turn, Active/passive decision
- Adelphos: Both abilities are during your turn, both are active/passive decision
- Harpier: Cleave is clearly during your turn and active, Iron Hide is defend, so would never apply
- Pteryx Maneuver: Defend, so would never apply
The other champions I didn't mention have abilities clearly during your turn and active.

Finally, regarding your concern about Randal still being useful if some abilities are excluded, I would say that even if NONE of the other Defenders' abilities were available to Randal and if the Safeguard ability were only available while ON the Plains, I believe Randal is by far the most overpowered Defender, because his action economy is incredible (when you can move less, you can do way more things) and even provides compounding value when the Coast is on the Dispatch side. For example I'm currently in a game with Coast (Dispatch) on the left and Forest (Enchant) on the right, and I essentially never need to leave the Capital City, because I can Dispatch my teammate and/or Enchant, and automatically heal to full so I can Sacrifice freely. I'm not only saving my own actions but also my teammate's. The game is on highest difficulty and I expect to tackle it very easily.

Let me know your thoughts and what you decide!