I’m not pretty sure if this topic is ok right here or if should be on General discussion, but I wish Team Balance read my suggestion and consider it to a future patch.
My suggestion is very simple, reduce the time of Corvid reactor upgrade from 79 sec. to 70 sec. Let me explain the reason of this change and remember that the upgrade won´t affect the Ravens in game, just the Ravens that you make when the upgrade is complete.
Actually Corvid reactor time is 79 sec.
Raven and Liberator time is 43 sec.
Viking and Medivac time is 30 sec.
If you open with a Liberator (followed by a Raven) and start to research the upgrade, the upgrade finish before the Raven and this is very good (86 sec. producing both units vs 79 sec. of the upgrade).
But if you open with a Viking or a Medivac (followed by a Raven) the Raven finish first to the upgrade (30+43=73 sec. vs 79 sec. of the upgrade). and the difference is just some sec.
The only way to solve this inconvenient is delaying the Raven production, but don’t think is the way of how this should be work. Best regards.