Like you said, does the Soon-Yi incident mean he molested Dylan? Of course not. But I would argue that it definitely establishes a pattern, at least in the eye of the public. Not to mention "Manhattan", "Husbands & Wives" and a few other films featuring Woody wooing young girls. None of this proves anything but I also don't think it should be dismissed as being unrelated and/or purely coincidental. And I'm sure many of the people who are speaking out against Woody and severing ties with him would say the same thing (even though actors who worked with him *after* the Sonn-Yi incident perhaps have a shakier leg to stand on).
One other piece of evidence I heard about that made it look like Woody was innocent was a taped interview with Dylan when she was a child. Apparently, not only does she sound like she's being coached but the tape was also noticeably edited.
I'm a big "innocent until proven guilty" person too- in most cases. Sexual abuse is sorta different- I tend to default to believing the alleged victim, at least to a certain degree (and it's important to remember that *a lot* of people feel this way, which has strengthened the the "Woody is probably guilty even though there's no evidence" stance), though obviously always try to get as much info as possible before making any actual assumptions. Sure, kids can be coached, even brainwashed but I'd have a hard time watching a child describe being molested or raped with tears streaming down their face and reacting with "Hey, the guy who you're saying did this to is is innocent until being proven guilty". Not that I would ever actually *say* that of course, but you get my point.