Keep forgetting about this. Looking at the Wikipedia it seems they had only just started development when they announced it. They really shouldn't have announced so early.
If I remember right, they went into full development since Spring 2018. Though, the Maniac Team is substantially smaller than the one allocated to Persona so no surprise for the time it is taking.
Also, the reason the announcement was made is because it coincided with the 25th anniversary of the franchise (Even older if you wanna count the Megami Tensei games)
Only fault from them would be the staggering lack of info in the meanwhile, like there hasn't been a single teaser released since the first official trailer they posted for the game.
They even went to the official Megaten Reddit to calm down the fans that thought the game canned,lol.
Atlus/Sega have serious issues when it comes to early PR and it's bothering most peeps.
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