That's a good argument for video games in general, but not necessarily a good argument specifically for Civ VI DLC content IMO. For the price of a few DLCs I could get a whole other video game. If you are a Civ fanatic (ie people on this forum) or a completionist, then maybe you get just as much value from having access to Ethopia, Persia and Poland as you would from a whole other game that you could spend hundreds of hours playing. But I suspect this is not the case for the general gaming audience.
Civ's popularity is based largely on its replay value, which is why it inspires so much loyalty from so many fans. Quality DLC (so far I'm very happy with the way VI is developing) adds fresh interest and a reason to replay a game that I already want to replay. I'd rather have one wonderfully detailed game than divide my attention between a half dozen others. Besides, there aren't many games that inspire me to spend hundreds of hours on them outside the X-Com franchise... which is also made by Firaxis.