You could, but that's not in the spirit of the scheme and all you'll do is wear out the battery and potentially lead Octopus to pull the deal for everyone else, for what? A gain of about 50p/day.
I disagree with your first point and your conclusion.
Octopus are no idiots and they are well aware that there is a number of customers who have battery storage units and could do just as you said. That is why Outgoing Octopus was previously “not compatible” with any of their EV tariffs.
They have chosen to reverse that decision (and not only reverse it but putting customers on a 12 month guaranteed export contract, so they won’t be changing their minds for at least a year!), which suggests they are grossly prioritising reducing grid load during the day. Increasing the export tariff nearly four-fold suggests to me they
REALLY want that day time juice flowing.
One of two scenarios comes to mind, then:
1 - They want the peak-time production so badly that they don’t really care if it comes from solar directly or from batteries filled during the night
2 - The number of customers with battery storage is so small in the grand scheme of things (which it probably is, and many will have export limitations imposed by the DNOs anyway) that they just don’t really care.
Either way, I cannot see how charging batteries during off peak time goes against the spirit of the tariff, they positively encourage it.
And I certainly cannot see that this will lead to scrapping the tariff, as you suggested.
I suspect there is a LOT going on behind the scenes between energy suppliers, generators and distribution network operators that we have no idea about.