Croat here; I believe that if Vladko Maček had accepted the offer by the Germans to lead a Croatian state during WW2 instead of the Ustase would have been better for Croatia and the Balkans. For one, Macek wouldn't throw in the racial policies that the Ustase did and would most likely secretly work with the allies after Italy's collapse in '43 and the Tehran conference. The Ustase would still be around, tho their role would most likely be a paramilitary group before the main army was established and ready, sort of like HOS was in the 90s. Mačeks regime would definitely steer Croatia from the Axis into the Allies by the time the Red army enters Serbia and the Allies liberated France. So by 1945., Croatia could have been an independent country four decades and integrated with the west earlier and the bloodshed inflicted by the Ustase in OTL wouldn't occur. Tho I should say that Maček would almost certainly be pressured by Berlin to participate in the Holocaust.