He’s not entirely wrong, based on what we see in Star Wars: A New Hope, it’s clear that nobody bothered to review the Death Star plans after they were stolen, which seems like a pretty significant oversight.
We already know what happens to the battle station, and of course, so does Kylo Ren.
His primary focus, however, is the general problem of the Death Star design.
Wouldn’t you go through them yourselves after they were taken in order to figure out what the Rebel Alliance might find?
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KYLO REN REACTS - Rogue One Trailer 3 (Final Trailer)