Why did the Romulans need Klingon D-7 Class Battlecruisers?

I know that traditionally the answer to this question was that during the TOS the Romulans and Klingons had an alliance where the Romulans exchanged cloaking devices for Klingon warships to supplement their own navy of either weak warships or non-warp capable ships depending on the story with this alliance eventually culminating in either both powers creating the B'rel Class Bird of Prey as a joint venture or the Romulans giving the design to the Klingons and them modifying it further. And while this was never canon it was the most wideky accepted explanation.

But newer series have been contradicting this more and more. First the show Star Trek Enterprise established that Romulans already had warp drives and the Klingons already had Romulan style Bird of Prey's a century before TOS. Then Discovery established that Klingons already had cloaking devices about a decade before TOS. Then the show Strange New Worlds established in the final episode of the first season that not only did the Romulans in the TOS era have warships capable of going toe to toe with Starfleet but they were able to sustain a decades long war with the Federation seemingly without Klingon Battlecruisers. So why did the Romulans need Klingon Warships in TOS?