As above - the airport is massively under-served and it was a good business opportunity for both of us. In our eyes, the move represents what many players cry out for with the regional model as 1 airline serves the commuter/short-haul network and the other the medium-long haul.
There is no difference in this than 2 alliance members sharing an HQ which has been common place in many worlds.
EDIT: Sadly people on AWS now seem to think every move is in someway underhand or cheating in some way. It's not meant to be an aggressive move, the demand is there to be served and the market suits us both. Through fear of starting an argument (as every other thread turns into) I will retreat from the general forum battleground and carry on enjoying my session in peace with others who I know feel the same after a hard days work.
Just so it's here in case this rattles on
In reality in 2004 (current game time) Helsinki had 10 million passengers passing through it.
Before we arrived, there were 3 airlines with an HQ there with a combined
One other airline has a base there with 14x aircraft based there.
Another airline has HQ'd there us since with 1x S340.
The airport is missing out of masses of flights and so that's why we decided to use it as a dual hub.