I think the question of why Connie could be said to be "better" had a lot to do with what the producers of the forthcoming stage show were actually looking for.
Musical theatre is incredibly demanding and I think you really can't compare it to just the ability to sing beautifully, which the majority of the girls couild do, definitely. It's a specific skill (or range of skills). Can you imagine having the ability to hold an audience of over 2000 people in thrall all evening with no gimmicks, just your talent?
Both Helena and Connie in the final (and probably one or two on the way) had those abilities. What Connie has is that little extra spark of intelligence in performance and the ability to convey subtle emotions that set her apart from the others.
By the way, I've been teaching drama and producing musicals for more years than I would care to admit and believe me, Connie had that little bit extra. If that made her a front-runner, I don't think it would be a cynical decision.