Flashes definitely help! I've heard the 6D does well with lower light, too. Great job getting the shot :-)
I shot a friend's wedding with my 7D in a dark church last winter, which was quite the struggle. The low-light performance on the body isn't great.
Yeah the 6D's aren't awesome at low light but we prefer them as they are lighter and we work better with them, and then use flash when we need! Not used the 7D but Canon are a little behind with low light atm, but will always stick with them now, after 8 years seems silly to change!