No, they're not. Forums and content aggregators are significantly different in terms of user experience and, frankly, project goals.
One of the biggest differences between Reddit and forums is focus. A web forum is focused on a topic, and has sub-topics. Content aggregators are flat, and focused on, well, content aggregation. They're a mix between link aggregators and blogs. The modern version of them also involves user created and maintained discussion groups, where forums have set sub-topics and generally have site-wide moderation.
And modern forums, FWIW, have threaded comment chains.
Reddit and Reddit-like services are really quite shit at being forums. There's very little about the user experience that they have in common.
So instead, it's "let's beg Lemmy to fulfill these use cases that it currently does not". Got it. Makes total sense, and is not internally incoherent at all.
Definitely not just arguing for a monoculture.