many services unfortunately go the route of trying to make an “everything app” which often leads to bloat

I wouldn't necessarily say that, it does work well for a lot of projects when used as an all in one package to have all development on, especially when it's a public instance for many different projects such as GitHub. There's just a lot of unnecessary parts and duplicated parts they have when specifically hosted for a single project, especially if there's other infrastructure already in place. It feels kinda like running an Active Directory domain for one user and one PC (which I'm ironically considering doing, except that I have three computers).

I will say that, compared to the usual git services (Gitlab, Github, Gitea, etc.) it is severely lacking polish.

I do agree. One thing I can think of is that it would be very nice to have a link back to the project from a linked repo. Currently something that's sorely missing imo. But they do say it's alpha quality though ;)

I personally despise bugzilla. It’s one of my least favorite parts about contributing to KDE. I personally find it very unintuitive, and messy. The UX of the service, on the whole, is not a pleasure.

I get what you mean. I don't mind it since I understand how it works, but for example I'm always apprehensive about clicking the submit button since I think maybe I accidentally edited some field I didn't want to edit. There's also some strange restrictions such having to upload attached files one by one and having to make a new comment for each of them. It's certainly got its flaws, but the nice thing about it is that it's a central bug database, with a lot more detailed categorization (bug status, dependencies, platforms, affected versions, product component, etc.) than what GitLab provides, which is pretty much just tags for all of those afaik, which is very valuable for a huge project like KDE. I'm not sure whether any FOSS alternatives that provide all that exist honestly.