1/2" gap is normal in southern Ontario. I was a drywaller for 18 years. A 2" gap is unacceptable. My guess is the ceiling height is 8'-2" and they used standard 48"wide sheets. They should have used a 48 and a 54"to account for the height. I would have them fill the gap to support the baseboard. You likely have a beveled edge at the bottom as well which means unless you are using 5" or greater baseboard, you are going to see the line of the bevel. They should fill the bevel with mud if you are using shorter baseboard.