Are you really going to dictate a ship's function by name? So if the only thing that changed was that venture was called "Venture-class carrier", would that satisfy you?
I'm dictating the ship's function by name? Not really. Mostly I'm just going by what the devs figured it would best be described as. Which is a cruiser. And given it has no more flight decks than the Condor despite being a whole category size larger, I can't really say I disagree either.
Though you do raise an interesting point - are the Condor and the Venture similar designs? Since I wanted to give your view a fair shake, I went Codex-diving to see if I'd missed something. Here's what I found. If you compare the Condor and the Venture side by side, I think you'll find that as carriers, they are neck to neck, but that the Venture has 150% more armour, 100% more hit points and approximately three to four times the firepower. This, to me, suggests they're not exactly made to fill the same kind of niche in the fleet doctrine if you know what I mean. In fact, arguably the Venture is
worse as a carrier than the Condor is, given it requires 33% more fleet points to deploy despite having no greater fighter support capability.
(As an all-around ship it is, of course, superior in about 90% of all cases, but that's beside the point here.)