WotC's leadership "failed" their way to 5e exponentially enlarging D&D's player base and cultural footprint. But those levels of growth were always unsustainable, so now they are trying to engineer a soft landing, unlike the crashes that have plagued D&D in the past.
Previously, this is when TSR/WotC would have announced a whole new edition to try to get the hardcore base to replace all their books and thus infuse some fast cash into sales. But they are trying something new, now, which is to engineer a shift to a D&D culture that is perennial, where they can put out, say, a new PHB without it signalling that everyone needs to replace all their stuff...or maybe quit the game (or just stick with the old version, which from a WotC perspective is more or less like quitting the game).
All of which is to say that I think it's a little early to argue that WotC's leadership has failed.