"already unable", is Houshou a retired kanmusu or something?

historically Houshou was the first commissioned ship designed from the keel up has a aircraft carrier with all previous carriers being ships converted from liners or other large warships (although the HMS Hermes UK's first true carrier launched before the Houshou was completed and trials finished sooner and was commissioned first.) and thus became the worlds first true aircraft carrier that was made has one from the start of design in active service.

however due to being among the first true carriers she had flaws in that she was small and could only carry a small amount of aircraft (around 15) as well has being unable to launch newer Japanese naval airplanes which mean she couldn't project air-power effectively so by the start of WW2 in 1939 she was reassigned has a training ship and mostly stayed out of the war which allowed her to survive it at the end of the war in 1945 she was used as repatriation transport to return Japanese troops home and then scrapped in the 2 years afterwards.

I already knew the gist of that, I meant in the context of this story.

Long story short: She can't hold the power ("advanced" armaments) to protect the world (fight the Abyssal Fleet) because shes too old but she still serves with pride.

Historically saying,despite being a Mother of CVs,she's outdated but that helps her survive the war.