Wasn't the A220 designed to compete with the medium size jet market? With 2-3 seating, and the -300 variant with similar capacity to an A319, B737 it seems to have been designed as a direct competitor to Boeing and Airbus.
What's AA's plan for an aircraft to fill the 100-ish seat market once the E195's are gone? After AA retires the remaining E190's, they have nothing to fit the gap between their 76 seat E175 and 128 seat A319. Delta was smart years back by scooping up all their 109 seat B717's. In fact, numerous airlines were scouring the market for used 717's and couldn't find many because DL grabbed them all, while laughing all the way to the bank with the high yields it offered. The 110 seat A220 is a perfect supplement, and possibly a long term replacement to their 717 fleet. An A220-300, with 120'ish seats will probably supplement or eventually replace their aging A319/A320 fleet.
It has an interesting history, none of which really makes it a true Airbus plane. From a pilot and maintenance perspective, nothing about it is common with any other Airbus model considering it was fully designed, tested, certified and put into revenue service with customers by the original manufacturer, Bombardier, long before Airbus took a 50.01% stake in the "CSeries" program that it was created under. Recently Airbus upped it's stake to 75%, with the Quebec government retaining 25%.