You’re certainly not overthinking it - it is very important to get the name right if you are migrating people from something else or attracting new people. We went through this process in the early stages last year.
“Discourse” got a big downvote because it was even more obscure than Forum (ok, our users are UK English and probably in the top half in terms of education level).
Lots of ideas were kicked around but in the end we settled on the “XYZ Forum” for the overall name, or “the Forum” for short. “Discourse” is understood to be the name of the underlying system (like say Windows, or Android or whatever) by those who come across it.
There was no apparent feeling that “forum” was old fashioned or tainted by previous experiences (most of our users, apart from the techies who set it up and run it, probably have never used bulletin board or forum systems in the past - indeed many are tech-phobic, but do have an idea of what a forum would be in general non computer terms). It could be that the Discourse experts here are themselves a bit stuck in a rut over this, but maybe things are different across the pond, and it’ll certainly be different if most of your users have experienced previous forum systems.
In addition it was felt that the term “category” for the individual discussion areas was unhelpful. We still call the dozen top level categories “Categories” but they are all read-only information areas with no live posts or replies. Everything happens in sub-categories which we call “forums”
The real confusion comes with getting people to understand the relationship between “groups” and forums. We have ended up with a pretty much 1-1 mapping between groups and forums which is much more comprehensible.
Incidentally we also use the term “Hub” for a central custom system that links together the discussion forums (long term, considered debate and information) on Discourse, and the instant messaging and ephemeral chat (for which we use Mattermost, but Slack was one of the alternatives considered) and file storage and collaborative editing - for us on Nextcloud. It has been a battle to get things like single-sign-on and more or less seamless working between the different system, but we are 80%+ of the way there.
Do involve your users in the decisions, but beware of only asking early adopters as they may well have more ‘baggage’ colouring their judgement.