Correct, none of the newer forum platforms offer THREAD (tree) view.

I like the option to have THREAD view but I am totally fine to do without it and just use the linear board view. I am not a developer but I would assume it is more difficult to customize a truly mobile responsive template that can handle Thread view effectively.

larum is my favorite because it does look very nice, if you read their intro, they say it is by far the fastest and most light weight, so I am not sure why it is not loading fast on your browser.

I tested Flarum both on my desktop and mobile devices, they do load very fast even for posts that have almost 100 posts in it. If there is a way to customize Mylittleforum to look and function more like Flarum, that would be ideal.