I think that if you annex a country by focus, like Italy can do with Albania, or by the puppet system, they should stop generating resistance and act like a core state.
I actually don't think so. Such a thing should only apply if there was an escpecially high percentage or even majority of population of the then occupier. I would say 50%+ would do it. Austria, the Sudetenland and Danzig (city and closer vicinity around it) are examples for such a case.
In the case of Albania there had indeed been strong ties to Italy from the past and there was a considerable Italian minority living there, but it certainly was not high enough to justify a core. It had been a protectorate of Italy and was more or less annexed but it was not Italian national territory by demography or long-term historical development.
I think that the ease of taking over Albania already is being reflected in the game via that there is no state of war and just an annexation - while in reality there had been some fighting over it which admittedly didn't last long and was half-hearted at best.
I however agree to you that Italy should start out with a higher degree of compliance in Albania when completing the focus. Time has long been due for an overhaul of the Italian focus tree...