The composition of night elf and blood elf survivors differ though. In the night elf case Sylvanas essentially axed what we're told is almost the entirety of their civilians. However, the actual army, especially the veterans, were away at the time and are mentioned to be larger in number than the army that the Horde struggled with in the War of Thorns.
With the blood elves it's different, since the Scourge was pretty indiscriminate and there is an actual civilian society plus military left behind. If I had to compare them, the night elves are capable of prosecuting war better than the post-Scourge blood elves, but their society is fucked in the mid to long term.