To me, the strength of traditional forums lies in the longevity of topics. Unlike Reddit and its fediverse clones, which have a sorting algorithm that prioritizes new content rather than old but still relevant content, forums present threads in reverse chronological order based on the last reply, meaning as long as people are talking, the topic remains seen.
Consider the following example. Let's say I'm on a classic car forum and want to post about a restoration project I'm working on. I start a topic, explain what I'm doing in the OP, and post updates as replies. Others can follow the progress of my project and give comments and feedback by replying in that one thread. The project may take months or years, but that single topic will remain relevant and visible for as long as the community thinks it should be relevant, demonstrated by myself and other members posting replies. In time the topic may become an enduring facet of the forum's culture.
Now let's consider the same project undertaken on a redditlike site like Lemmy or Piefed or indeed Reddit itself. The default sorting algorithm causes posts to appear lower and lower down the list as time goes on. It also takes votes into account, which is another bone of contention I have with these platforms that I will address later. Anyway, I make my OP and others comment on it, but after a few days it's buried under newer threads, meaning new people (or old people who don't bookmark it) will probably never find it. The only solution is to post updates as brand new threads, which makes it hard to follow for newcomers and fractures the discussion. If I want to post updates frequently I end up spamming people's feeds and crowding out other stuff. On Reddit they even lock posts after six months, further aggravating the issue. I've experienced this firsthand, posting similar topics on a traditional phpBB forum and Lemmy. The phpBB thread hasn't left the front page of the subforum in the 2 years it's been there, with plenty of discussion by other users. Meanwhile, the Lemmy thread plummeted to irrelevance after a few days and I had to post new content as new threads, clogging the feed.
The multithreaded nature of comments on redditlike platforms also means you can't reply to more than one person at a time, you have to make multiple replies under each comment you want to reply to. This is in contrast to traditional forums where you can quote multiple users. Now this is potentially where redditlikes have an advantage. Even though you can't reply to multiple posts at once, multithreading replies makes the post as a whole easier to search by hand. Each top level reply can be it's own little mini post, and replies to that reply are sorted directly under it. While this makes the overall timeline of posts hard to follow, it makes it easier to find specific information because off-topic ramblings are clearly marked as long comment chains. When I bring up how I miss traditional forums, this is what people seem to bring up most often, that long threads that go on for years are hard to follow because they're discussing a completely different thing on page 33 vs page 1.
As for the voting system, I think it can have a place when searching for solutions to a problem or looking for advice, especially when you're not familiar with the subject and don't know what's good advice and what's nonsense (RIP YouTube dislike button). But outside of this narrow context I think voting systems are harmful to the community. They encourage echo chambers and reduce engagement to making a number go up or down. On a traditional forum if I want to express my opinion I have to post a comment. With a voting system it's just a number. They also feed social media addiction because monkey brain like number go up, and you can see this firsthand with karma farming on Reddit.
Such a seemingly little thing as the default sorting behavior of topics drastically changes the community's culture. On Lemmy at least, you can replicate the traditional forum experience by sorting topics by "latest comment" and even mimic the flat single-threaded comment structure in individual posts by using the "chat" option and sorting by old, but nobody does that, so the culture develops around the default.