I am trying to come from as objective a point of view as possible. I enjoy history rather more than myth-making.
Why a miscalculation, Edward had thought leaving behind the elderly and incompetent Warrenne with several English garrisons was enough to hold Scotland.
Much of what you call cruel and vindictive about Edward, was policy. Nothing terribly unusual there. No matter what your political slant is, there's no denying Edward was capable. Bruce was enormously capable too, his character notwithstanding.
Wallace was a very big menace. If Scotland were restored to independence, with an hostile king, the political consequences would be enormous. He had already tried to call on the Kings of Europe and Rome for aid.
Of course, I must be an imperial lackey.

John, some Australian recently, can't remember if he were a psychologist working for the police or what, had looked at Kelly's famous letter and said words to the effect of it being the whiniest, most adolescent thing he'd read in his life. GROW UP with how he summed it.
I'm of the view that one should try to gain as good an understanding of historical characters as possible.