That's a very simplistic view of the situation IMO. There are more variables than low/high effort at play.

I'm familiar with that study you mention. The hottest women get the most messages from guys. I'm sure that includes high and low effort messages. All things equal, it's unclear to me whether odds would necessarily improve with a high effort message as I think you're assuming a high effort message will include a message that is positively received. Saying "hey" isn't original but it is very ambiguous in the sense that the receiver doesn't really learn much about him. Say the sender sends a few sentences as an initial message and misspells something accidentally. Now the receiver might think he's an idiot. Or maybe he makes a joke and she thinks it's dumb. Or maybe she's overly sensitive about one topic and he unknowingly made light of it. High effort messages can be received poorly is my point.

Further, in my experience, the hottest chicks place the most emphasis on looks... And that's cool. They can do that. They have hundreds of messages to filter through and pictures are a quick way to toss out a huge chunk of them. In this case, I doubt she even considers the content of the messages. In POF, for instance, I've sent plenty of messages that get deleted that haven't ever even been opened! Again, I'm not complaining. Rather, explaining the dynamics here.

As for average women, they certainly don't have hundreds of emails to filter through so they're more likely to read the message. I think it's probably a fair assumption to make that most of these women will place more emphasis on the message's content than hotter chicks but you'll still have the problem I mentioned earlier about the message possibly communicating something disagreeable. But even if we assume that that doesn't happen (ie all high effort posts will be positively received), the change in the odds of success is probably negligible. Women don't accept dates just because you wrote 3 sentences instead of 1.