That one is optimized to be a web site and the other is optimized to be a personal note-taking platform? ;P
A markdown document (e.g. from Obsidian) can be hosted as easily.
Yes, but the tiddlywiki file is the entire wiki. You've perhaps tried the dataview plugin for obsidian? Tiddlywiki is built on a similar idea, but much more flexible and powerful. However, tiddlywiki doesn't support in-text definition of fields (as far as I know)