I would argue that it is an ethical thing to do so if it sends a signal to pay whitehats appropriately.
Burger King is almost certainly going to experience no damage from this.
Their takeaway will likely be entirely non-existent. They’ll fix these bugs, they’ll probably implement zero changes to their internal practices, nor will they suddenly decide to spin up a bug bounty.
“The signal isn’t to pay white hats more, instead…”
And perhaps an addendum such as:
“…which will then, indirectly and in the long run, create the signal you were replying to.”
Appreciate your clarification despite the bluntness of my reply.
Also, you’re probably right, the signal will likely pass right over Burger King’s crown.