Does simple paper take less time for publishing?
In general, no. Most of the time you wait for your paper to be accepted or rejected is waiting time and process time, not review time.

First, it sits in the editor's queue until they can review it. Then, they have to find and solicit reviewers and wait for their responses.

Then they send it out to the reviewers. Then it sits in their email or on their desk until they get around to it.

Finally, they review your paper! Then type up notes and send it back. A long or a short paper or quick or hard to understand will only change this time chunk here.

Then their response sits in the editor's inbox until they read it, make a decision based on it, and pass it on to you.

(Plus repeat for any additional rounds of revision.)

As you can see, most of the time is wait time, not affected by the length or the complexity of the paper.

I've had papers wait months on a reviewers' desk.