Fair points indeed.
You also need to factor in your 'Daily Supply' charge, 'General Usage' tariff and if you have a second smart meter, 'Controlled Load' tariff. Not overly difficult to work out your best case scenario ... although Excel is your friend.
I haven't seen the first bill yet to confirm, but it seems Origin are not changing the tariff to 8c/kWh, but rather giving me a credit for the difference between the rate they normally charge (for me 22c/kWh) and the 8c/kWh when charging the car.
Your OVO plan seems good and one worth looking at.
I think we are in interesting times. More and more EVs are coming online and the electricity retailers have realized this is a new competative market they can tap into and are throwing carrots at us to win our business.