The terminal separation between international and domestic is done with. Old domestic terminal is now called "Terminal 1". It is mostly used by Star Alliance flights. The old international is now "Terminal 2" and is used by One World mostly. Ex Schengen flights are still where they where prior to the re-organisation in 2009.
As for the traffic congestion, well more runways available than LHR and frankly the traffic is lesser, I would put the so called afternoon rush hour to ATC inefficiency within the Helsinki TMA. There is really no reason for holding with 2 parallel runways and a 3rd cross that could easily be used for LAHSO operations by commuter aircraft with proper planning.