Artemis might use a swipe gesture to visually hint at the relation between upvoting and boosting, as shown in the main animation. Here’s a static app mockup with both swipe levels displayed. I’d also imagine that there should be a setting that auto-upvotes posts when boosting.
As far as I know, it really is primarily a share button. While it does give people 2 reputation points (which I don’t think people should be caring about), the main purpose of the boost is to be a retweet button, not a super upvote. That’s probably why it’s set aside on the UI, and it’s probably why it has the same name as Mastodon’s retweet equivalent. This visual you have looks cool, but I think it changes the UI from unclear to misleading.
I think that’s how it functions for Mastodon, but Lemmy and Kbin use boost more as “+2 upvotes”, as it’s used as the scoring metric for the sorting algos.