Who doesn't have plots in this book? I hardly think that's a test for evil in this book - more like a test for intelligence.

Not the best test. Ron is intelligent. Ron does not appear to plot, only form and employ strategy.

Assuming that it was all a Quirrell plot - which I do at this point - he could also have redeemed Hermione at the last minute with some evidence after she was condemned, and his point with magical Britain had been made.

Like he did with Harry against the Dementor.

Like he claimed he intended to do with the auror he threw an AK at.

Like he did in the Draco the Drop Lord Theatre incident. We should be suspicious of that one, as well.

Like he did as Voldemort when he set his Forces of Evil up to self destruct after he left the game, thereby sparing the rest of the world.