In universe... Why would Romulans need Klingon ship designs?

[MAGolding]

But he only ended up with two ships...

Four minus one equals three.

UHURA: Sir, sensors are picking up four Federation starships. M-5 is altering course to intercept.

SPOCK: The Excalibur, a direct hit.
CHEKOV: Closing on the Lexington again, sir. The Hood and Potemkin are moving off.

KIRK: Battle status?
SULU: The other three ships are holding station out of range. The Excalibur looks dead.

 

[Samuel]

I always wondered why the starships Hood and Potemkin seemed to linger within range of the Enterprise for so long despite the pounding Lexington and Excalibur were taking.

 

[Phaser Two]

I always wondered why the starships Hood and Potemkin seemed to linger within range of the Enterprise for so long despite the pounding Lexington and Excalibur were taking.

Because they probably didn't know what to do. It was a pretty unusual situation.

 

[Timo]

...To begin with. I rather doubt Starfleet ever intended to fight with three or four cruisers against a single enemy counterpart - this is just how they set up the least-variable test on the capacity-multiplying potential of M5. The four skippers might in fact have been at loss to effectively coordinate their multiship attack, being more used to outgunning enemy cruisers three to one and fighting them solo.

When M5 went haywire, it just confused an already stressful situation...

Timo Saloniemi