CoH was in development for about 4 years before the public could play it.
CoH development was a bit twisty. It started around 1999 if I recall correctly, but it was conceptualized as a much different game than we actually got. It was around 2002ish that CoH original recipe was abandoned and development shifted to CoH extra crispy, or CoH-lite as it turned out to be. CoH-lite was built upon CoH original recipe to be sure, but it was worked on from about 2002 to 2004. Arguably, it was worked on until 2005 because CoH launched with actual core features incomplete or non-functional, such as task forces or all of the levels from 41 to 50.
Also worth noting that "CoH" is both a game platform and game content. A lot of the launch-day content was undoubtedly worked on from 1999 to 2004 but its possible most of the core engine was completed by 2002. Much of the powers in the game and the entire archetype system dates from after 2002, as the CoH original recipe was more of a free-form character system. Archetypes are a concession to CoH-lite.
CoH development is instructive in a different way than just looking at the development time. The devs fundamentally had no idea what they were doing, when you really get down to brass tacks. As a result, the game concept was virtually impossible to implement in any reasonable time. It took a major refactor to give us any game at all. And those were professionals. Volunteer groups have the benefit of having actually seen a functioning CoH, but they have similar challenges. The first one you make is never going to go smoothly, because its almost impossible to know if anything you're doing at any time actually makes sense in the bigger picture until well past the point when you've spent tons of time finishing it. Lots of things get scrapped or redesigned to take that into account, and that can turn game development into Brownian motion. It can seem slow even when its moving fast.
I would argue that even the second time around is not trivial. Keep in mind the second time around for Cryptic wasn't Champions Online, it was the never-launched Marvel Universe Online. Champions Online was the *third* outing for Cryptic, and even that didn't go smoothly.