A few things. First, it would have been foolish to put Clark an O'Hara against each other. Clark was the clear winner out of the gate. O'Hara had a much better chance in Featured ( and should have won for her brilliantly nuanced performance over Ramirez who gave a showy but one dimensional performance). Also, featured really isn't the same as supporting, at least in my book. Since Clark and O'Hara were both below the title, they had to petition Clarkbto leading. It just made no sense to try to get both ladies up there. And while Clara is central to the plot, it's really Margaret's story being told. But there are many cases in Tony and Oscar history of performers being put in featured/supporting category so 2 in the same show aren't against each other and likely splitting votes. I don't think this was one of those such cases.
"Broadway...I'll lick you yet!"