This may have been mentioned before, but in case it hasn’t…
So is Obsidian justa Wiki?
There is a difference between a tool and a methodology.
A wiki is a tool enabling you to write and connect notes via `[[Wiki links]].
Obsidian is a tool enabling you to write and connect notes via `[[Wiki links]].
So looking at them as tools, yes. Obsidian can be used to build and manage a personal wiki, pretty easily.
However…
What you do with those notes is what changes things.
Methodologies such as Zettelkasten, LYT, and many others can be used with a variety of tools. Then it becomes a matter of how well the tool supports the methodology.
Obsidian arguably better supports these methodologies than a simple personal wiki tool. But you can implement these note taking frameworks within something like TiddlyWiki if you wanted to.
Just remember to separate the two and think of them as independent but complementary things.
Decide what methodology you want to use, then select the tool that best supports it.
If you are undecided on a methodology then you should select a tool that supports many methodologies quite well.
That describes Obsidian.