You're missing the point. Each character takes a year to create. Nothing you said really matter. You're telling me that only a few months ago they started work on Mewtwo, and in less than a year he's in the game?
No, Sakurai directly told us he just started working on Mewtwo's actual game data besides his base model around the start of December. This is official word. Seriously, it only takes a year when tons of stuff in being worked upon. There is no way it takes a year for a single character and then for Sakurai to outright start him(officially) in December and expect him less than six months later. He's clearly not going to take that long. Sakurai is sometimes bad at wording stuff. He didn't make it obvious that it does take a year during busy periods, which is the most logical thing and explains exactly why Mewtwo is going to take about 4-5 months at most.
Take into consideration that DLC is worked on even during initial development. What, right as soon as MK8 was out, ALL that DLC we got was started in in June and completed just now? Fail logic on you.
You mean Mewtwo and that's it? Do some research. None is being done besides him. At all. He also directly told us this. Like, today(no more balance patches are going to be done unless something extremely bad comes up. He just admitted that he's done working on the game beyond Mewtwo. More than once he even said Mewtwo is the only current DLC.). The Miiverse stage is already complete, it just needs Miiverse people creating fun phraes to add on. It takes literally about 5 people max to keep an eye on funny Miiverse phrases to add on. And then boom, done. It's just Battlefield and he even showed us he had phrases already done.
How many times does Sakurai have to outright tell you that Mewtwo is his only thing being worked on till you understand this? He will not take a year unless Sakurai somehow is put into the hospital, making it impossible to complete him on time. He'll be in as late as May. Guaranteed bar the one potential exception noted.(or, you know, some executive meddling actually stopping Mewtwo from being put out at all) The time needed is far lower. Complications beyond that are possible, but they're few and far between. It's also obvious why he's not doing more balance patches, so he can test Mewtwo against the currently updated cast and have a solid thing to work with. With less testing time needed, he can get him done faster. He also has more members to work on the character, nothing else to work, and zero implications he'll be stopped from working on him constantly.