I think more content for all ships is inevitable anyhow, down the line (probably just before release, as the mechanics take precedence at this point). I don't think wanting more hulls and superstructures at this point at the expense of improving core game mechanics is a good idea, in my opinion (that being said, the more hulls and superstructures, the better).
Adding corvettes, however, would bring some fresh air to the entire gameplay loop, allowing for more strategy options, and make for a more realistic experience.
Those ships did exist, and indeed, were indispensable - the game would be an incomplete experience without them. I wonder how the devs plan to tackle mining and anti-submarine operations without them, to be honest.
Gameplay wise, at least in the early access stage, the corvettes could even simply recycle Destroyer hulls and superstructures, but without the requirement for included torpedo launchers, and with buffs for mine and submarine warfare.