“Renly didn’t throw in his lot behind the Tyrells, the Tyrells threw in their lot behind him, as we see when they support his bid to become king.” Well yes, but the original plan was Renly doing a lot of the work to make the Tyrells the de facto lords of the realm, with himself as their useful hand.

I wouldn’t quite go that far. Renly’s plan was for himself and the Tyrells (because Loras’ swords and Margaery’s virtue are also included) to work to make the Tyrells and Renly the de facto lords of the realm. At the end of the day, he’s still a prince in the direct line of succession, the Lord of Storm’s End, the Master of Laws, and has the inside track to becoming Hand of the King.