How influential was he in helping mobilising public sympathy for the Greek Rebellion or War of Independence depending on which side of the fence you were on?
Well Philhellenism wasn't just limited to Lord Byron: most people who had a classical Western education (i.e. the ruling classes of Europe) would also have been very sympathetic to Greece. This meant that everything - news reports, diplomatic missions, public opinion - would have been tremendously biased in Greece's favour. Nothing that the Ottomans did would have been justifiable, in such a case.
And even if England and France didn't do anything, Russia would. So Greece was going to be independent one way or another.