Linked Mastodon posts redirect back to lemmy.ca son can't check, but going by the intro, it's something I've been noticing, when I boost a post on Mbin, Mastodon displays as you described, at most including the image as attachment, and that despite of the original post's instance.

However, maybe something like what Misskey instances do would be a good solution? For example:
https://nijimiss.moe/notes/01K5T7RE2G147ZRBSZ4GDHS3NR
(For https://thebrainbin.org/m/auster_info_dumps/t/1095421)
(Just don't like the links appearing again as attachments at the bottom)