"Titan" was to be a MMO, they actually stated this, the killed it because the market isn't there for another MMO
Overwatch had nothing to do with it
Titan had two components, MMO with crafting and jobs (one example was being a chef) that they compared to The Sims, and an FPS component where you go around the world (like an Egyptian city/pyramids was one example I believe) and do FPS stuff (they compared this to being like superman putting on your cape, normal 9-5 life -> superhero). It's readily available info that the FPS assets for Titan were spun off into Overwatch. In fact I read about it so long ago I don't recall the details anymore. googled this article from before the overwatch announcement
http://kotaku.com/heres-what-blizzards-titan-actually-was-1638632121 "But it doesn't seem like we'll ever see the Team Fortress 2-meets-Destiny-meets-The Sims-meets-World of Warcraft chimera that Blizzard was working on for so many years."
Also the market for mmo's is not mentioned as a factor by Blizzard's CEO, as instead Mike Morhaime said the game was cancelled because it just wasn't good enough. "We didn't find the fun," he said. "We didn't find the passion. We talked about how we put it through a reevaluation period, and actually, what we reevaluated is whether that's the game we really wanted to be making. The answer is no."
I think the real news story for Overwatch is that they are charging $40 when their competition is either free or under $20 (TF2 free, CS GO $8 on sale, etc). Maybe Blizzard could command a bit more for their games 5 years ago but I don't think they can anymore. If they don't have an option to play a limited version for free then I don't think I'll gamble $40 on it given their recent track record (Diablo 3 was beyond bad imo, while WoW has gone 100 miles in the wrong direction). It seems foolish to me to put up a $40 barrier when the cosmetic microtransaction scheme is so incredibly effective for lots of other multiplayer games.