The 1.8M Bretonian marines would be an overkill even if Bretonia hadn't been in such dire situation at the time. I think it's safe to assume your ordinary House military personnel is better trained and equipped than any force the ragtag locals of Gran Canaria could scrounge up. Not to mention the support of an entire battlegroup (however ancient its flagship may be).
Still puzzled how we ended up with the number of marines equal to more than twice the entire population of GC. An oversight by those in charge of the story, perhaps? Wouldn't mind, if the 1.8M number got retconned a bit (or explained to be Bretonian propaganda).
