I don’t know whether intellect was weighed as a factor or not. I suspect intellect was to a certain degree a factor. There is no doubt Obama was popular and even then a good speaker. However, intellect itself clearly was not the overriding qualification. And I don’t think anyone would say Obama was the best student or intellect in the running.
Also Obama wasn’t selected, he was elected. Albeit elected by the other 61 editors. Imo a selection when not made exclusively on merit would be arguably be even more suspect. Anyway, yes, elections are popularity contests.
From what I understand at the time Harvard was very interested in easing racial tensions. In fact, the first black tenured professor resigned over the situation there. So the election of the first black editor of law review would and did help ease some of those tensions.