Making proper hammerheads have always been a problem in AH. I don't know why, but it's one of this game's little quirks. What you should ask yourself instead is: How easy was making hammerheads in the real Typhoon. When you have that answer you can start making comparisons to this game or the other. Making a comparison between two simulations without knowing the real-life baseline is pointless.
Hammerheads are super easy in a 38 in AH. The only issue you can really have is bad timing on the throttle/rudder. Even that just makes you wash out a little at the bottom.
I really don't have a dog in this fight, but if someone tells me a Typhoon in one simulation hammerheads like a 38 in another, that doesn't inspire confidence in the flight model. You bring up a valid point, though. We have no hard data to look at, but seriously, does it make any sense at all that a Typhoon could be as stable and responsive in low speed vertical maneuvers as a P-38?