Over-powering the Klingons
Why did the Klingons have better ships at a time when they were less technologically gifted? Explain to me how this giant ship, the Sarcophagus, long thought lost to time, and was at one point a wreck that Klingon children played on, was able to go toe to toe with the U.S.S. Discovery, arguably the most advanced ship in the fleet at the time of the show's creation?
The ship was huge, it was daunting and it didn't belong in the time period that it was shoved into. I've said before and I'll say again that Discovery really screwed up by trying to "improve" the past. So many of these ideas, including the Klingogn Sarcophagus ship, would have worked so much better if you had set Discovery after the return of Voyager to the Alpha Quadrant.
You could extend the mythos, change things up, and put your own stamp on things, but instead, the introduction of this giant ship just felt like the writers working on Discovery weren't actually Star Trek fans or weren't writing for actual Star Trek fans.
Not only does the Sarcophagus not make sense as a ship in the time period, but giving it cloaking abilities also prompts the question as to why we have a different story about when Klingons were able to start adapting cloaking tech to their ships.
Plus, if Klingons were so talented that they could make this monster of a ship, that was quite formidable, why didn't they just make hundreds of them and squash the Federation? Messing with the past the way Discovery did cause so many franchise-shattering plot holes that just can't be filled in without some serious wish fulfillment.