You should really gain a blueprint for CVLs when you research CVs of similar year. Currently, there is almost no point in researching CVLs at all, as the CLs of the same year are far superior in literally every category except naval detection (they are better at fighting ships, subs, aircraft, which is pretty much everything). The ONLY use i could even think of for a CVL is for sea detection values, since CLs are better in every single category that you would use a CVL for, including sub and air detection. It might be nice if your carrier research gave a blueprint for CVL research, to give insentive to research these CVLs. Who wants to take up a tech slot for 4+ months to research something that you have situtional use at best for, when you could research something like a new land doctrine/infantry model (since the CVLs research years always come up at the same time as these important techs).