Arso, Menachem, re; gaon and baal hatanya:
I didn’t attempt to prove the gaons status from litvishe sources – there were no chasidishe sources in the gaons early life, because they hadn’t came yet! I’m referring to what the other gedolim said of him before the talmidei habaal shem were known
As for the baal hatanya receiving such a smicha, I don’t doubt it – he was one of the biggest achronim for a reason; everyone agrees to this, and the mishnah berurah cites the shu”a harav quite often for the same reason – he was , even among achronim, huge in ways that make this whole conversation a little bit unnecessary, because we have zero understanding of what these levels are to begin with.
But at the same time, i wouldn’t say that the baal hatanya could be compared with rishonim, while the gaon was indeed placed in such a category by his contemporaries. That doesn’t mean that every gadol from then until now has agreed to this, so it might be true that other gedolim(especially chasidishe ones) may have argued. Some said that the shaagas aryeh was bigger than the gaon in nigleh and that the gaon was bigger in nistar(and the shaagas aryeh did indeed argue with rishonim sometimes); this is something i also have no hasagah in.
So while in general comparing gedolim is a waste of time, i think the Gaon is an exception.