However HP nerf is unwarranted. Its 110 fuel, why should it die so quick? What 110 Fuel unit dies in 2 shots, tell me?
Consider that the Stuka is 100 fuel and dies in a single shot.
It's more about the units' role rather than the price: Rocket artillery is expected to be in the backlines, such an unit being too tanky makes it unreasonably hard to deal with due to you necessarily having to dive for it (This is also coupled with the limited timeframe you have to perform your dive, in many cases: Properly microed Rocket arty fires, and then scuttles to an even safer position until it recharges).
I'm honestly of the opinion that the Calliope should die in a single shot, but I might agree that this should be accompanied by a price decrease.