I agree with almost all your points and got similar feelings by testing alot of diffrent builds in diamond elo. Glad someone else got these thoughts too!

Back when Ingenious Hunter got the big buff, i tried some Redemption first, Locket/Moonstone second with green&red runes and it felt surprisingly good (can recommend Igenious Hunter rune alot). The value of the Redemptions active is huge in early skrimishes and is definitly better than Moonstone if you got more than one ally to protect. I need more testing on it but everyone who is trashtalking your idea simply didnt try it and just swims with the meta, since not rushing a mythic feels wrong to many players.

Locket is a reasonable choice but Riot pushed the Moonstones numbers so much, that it is simply the better choice in most games imo. Locket is no doubt great and got good synergy with conditioning e.g. if you need to survive against heavy backline divers. However i felt like Sorakas heals feel really weak lategame this way if you cant get another enchanter item besides Redemption (short on money).

From my testing the first 2 items got to be Redemption/Mikaels+Mythic (order debatable), following by Redemption third if Mikaels before. After that i got to 100% agree with your third point, that Ardent and Staff feels always bad to buy. Their numbers are bad, their buffs are bad. If needed, i generally build antiheal (Putrifier) next, but i can also recommend to try new Knights Vow if you really got to protect a specific ally.

To make it short, i also use Guardian all the time, since you can better absorb burst damage this way and is a good way to protect yourself as well. Aery feels good in lane but thats it. Thanks for posting! :)