I do think they're blowing the 200 hours out of proportion, and Chris Priestly even commented on this on the official forums. His entire comment could essentially be boiled down to, "Everyone will play the game differently, and some people will take 50 hours, others might take 200 and some perhaps even more than that". The best metric to go on is still the one they've stated the most over the years, and that is 50 hours Main Story, 50 hours Side Quests.
Considering The Witcher 2 was a 30-50 Hour game, add another 10-15 on top of that for entirely new content you miss because of choices/consequences and they were STILL able to achieve some of the best questing in any RPG, with the least amount of generic, boring collecting/fetch/kill shit I've ever experienced. I personally believe they've got skilled enough Quest Designers and Writers to be able to pull it off in The Witcher 3 (And the increase in developers at the studio) and create 100 hours of actual interesting content.
Although I do also completely understand folk who are sceptical about it. It's their first foray into an open world, and we've seen some awful examples over the years of games tacking on bloated, shitty content to fill their (open) worlds (Ubisoft, DA:I, and even going back to Skyrim), which gives enough reason to be cautioned.
As you said, all anyone can do is wait until May 19 and find out. Nobody really knew for sure if DA:I was going to feature so much shit until it actually released, and the same might be the case in TW3, but I sincerely hope not.