You are comparing Latest to a list of categories. Apples to oranges. I know you know this, you even addressed it.
As for the benefits of a presentation à la myBB, I’d say even though it is cleaner, it is also way less informative. I also felt overwhelmed the first time I had seen Discourse, but now I wouldn’t go back to the legacy way of presenting topics. I agree some things could be hidden or toned down to make it clearer, but not to the detriment of information. Compare the density of relevant information for someone that is looking for interesting/relevant topics (highlighted in red):
If you argue that some people prefer to drill down inside categories to see the topics that are relevant to them, then they should bookmark that category instead of the whole forum.
I feel like I’m not making sense but I hope you understand.