Had King George III been as willing to shed blood as Lincoln, George Washington would have been ultimately beaten.
Not really. Tarleton and other British commanders could be quite brutal. What changed was the nature of war. 19th century war became mass war with much greater firepower.
Howe was more of a begrudging commander than the King could be credited with.
Some Unionists despise McClellan, and in fact he and Howe share much in reluctantly pursuing the enemy. They were “kindly”, feeling a bit sheepish about coming down on their respective brothers.
As far as Washington himself being crushed, maybe, but he should at least get the credit of Lee who did lose. His troops were in MUCH worse condition than any given Confed unit, including the logistics of recruiting them and balancing all the different types politically (not just all units of a single “army”, but many levels of origin and funding, as well as all kinds of uniforms and non-uniforms). Overall, GW’s situation was much more dire.