Just from quickly poking around, I think Boost only alters the comment order for kbin instances. Lemmy only seems affected by upvotes & downvotes. Lemmy also seems to give each post or comment an automatic upvote (or maybe that is just lemmy.world, idk), whereas kbin does not do this. I am also not sure if the automatic upvote transfers between kbin and Lemmy. This all being said, I could also just be completely wrong and misinterpreting things lol.
As a side-note, I can only seem to get my posts and comments to show if I boost my own post… I am not sure if that is just a kbin thing or something unique to my particular instance.
Interesting. I do not have a mastodon account, but I wonder if this is not why boosting a comment or post might accelerate federation? I have noticed that (some) of my own comments or posts do not show on other instances unless I boost them myself, which not something I prefer doing as upvoting/boosting my own post seems kinda weird…