I agree. I believe forums that exist to support a product (like software) or to support a service will probably have better odds of good engagement numbers over a shorter space of time. Especially if you write software with a lot of bugs, jk! 
Compared to a forum created just for general discussion and community around a topic. My forum is the later. There are no support threads about something sold or something downloaded or anything like that. Just a topic for discussion and community.
That said, over a longer period of time I’m of the belief that advantage will become less and less.
Because with forums no matter how long it takes, there’s a certain level of activity (activity threshold of daily new posts/topics) that once you get over that level, all forums, regardless of reason for existence, will find that growth and activity will follow.
March 22 of this year will make 2 years with my forum, it’s a slower grind to get those core active users. But the last 2 to 3 months it’s starting to catch on with about 4 or 5 members really enjoying checking for content daily and replying and sharing.
From their lead, that it’s caused those members from 2022 and 2023 to return and be more active, even if it’s not daily.
Or in short, some use forums to support their brand (product, service, etc) while others use forums to build one. The latter can be a bit more challenging to get going but the DAU/MAU can be just as good over the long term.