Should a chainsaw go dull so quickly?
Yeah, when I first started using chainsaws, I was naïve to the idea of "sharpening a chain". The very fact that you were able to get 9 hours out of it tells me you were like me.  My first chain, the chain cut subtly worse and worse and worse and worse, and I didn't realize it, because like the frog in the cookpot... until I couldn't stand it anymore. 

First I paid the local lawnmower shop to sharpen them.  Then I discovered my local Stihl dealer would swap me for a new chain for $10. After about 3, he sold me some chain files.  Then I found a $6 flat file holder that makes filing much easier.  Files are a consumable, and I don't even try to adjust chain height: when the height is low I just go back to the Stihl dealer and get a new chain. 

Now, I can't stand how badly my chain cuts after even an hour. I typically give it a quickie sharpen everytime I add chain lube, and it cuts like a lightsaber again.