person_aggregates is interesting, because it is tracked for all known person accounts on the server. Where site_aggregates does not track all know instances on the server.
Personally I think lemmy-ui needs to be revised to clearly identify that a profile is from another instance and that the count of posts, comments, and the listing of same is incomplete. If a user from another instance is being viewed, you only see what your local instance has comments, posts, and votes for. This will almost always under-represent a user from another instance.
PREMISE: since person_aggregate has a SQL UPDATE performed in real-time on every comment or post creation, I suggest we at least make that more useful. A timestamp of ‘last_create’, either generic to both post or comment, or individual to each type. I also think a last_login timestamp would be of great use - and the site_aggregates of activity could look at these person_aggregates timestamps instead of having to go analyze comments and posts per user on a scheduled job.
And I learned just yesterday (TIL) that Lemmy does keep a real-time karma score on person_aggregates for both posts and comments. lemmy-ui just doesn’t choose to show the information. But there is no reason bots and other apps can’t use it as a karma value.