FWIW, I don't agree that this was LI's "best feature," nor do I share your dismay at this change. I used the feature a few times and thought it was okay, but I wasn't a huge fan. Because it really wasn't integrated into an individual user's experience, people had to make an effort to engage there - and I would venture to say most didn't. I also saw a lot of people gaming the feature, which detracted from its appeal.
I suspect LI has plenty of data and analytics to support their decision, as well as their recommendation that people use the group and poll features instead. I agree that groups have their challenges, but poor quality in them is generally the result of poor management. And the limitations you ascribe to polls can be managed as well. I've seen them used very effectively countless times.
I also disagree about the effectiveness of the Events feature. I never once saw it drive traffic in any appreciable way. Like the Answers feature, it wasn't sufficiently integrated into the user experience. I'd love to see an Events tab get added to groups, which could reduce a lot of the noise that currently occurs in them. The Q&A feature is effectively already built into them via Discussions.
One of the challenges with any of these platforms is "feature glut," so I think making a conscious effort to scale back is a good thing. Too many choices is too overwhelming, and we need to see more emphasis on quality vs. quantity. Everyone has their favorites and no change will be universally welcome, but I generally trust that LI is making a strong effort to optimize the platform in ways that make the most sense for a majority of their users.