Spigot replaced with ball valve- now the water gets out like from a water cannon...why?
The ball valve offers a straight through path for the water. It's bore hole is highly likely to be smaller than the feed pipe behind it so the bore acts like a hose nozzle. 

The older style faucets have a complex path flow for the water through the device which causes turbulence in the flow and also a pressure drop. This is what makes it look to you that the flow is somehow more gentle.