Should threads be included in conversations or should the tabs themselves be removed and display only one feed? 

There are so many replies that adding threads to conversations will almost certainly make new posts invisible or just very hard to find. 

 Not sure, maybe a third tab "combined"?

Maybe only available in the following feed? 

 Maybe you're right, there's always much more comments than OPs. I see why you have made the decision now. 

Thanks