Yeah, much like long-dominant titles in other genres, only FGO could kill FGO. The massive slowdown in meaningful content pretty much created many of the other problems. Hard for a character to be memorable if they don't appear in any story content which matters. When there's no new story content, people start to notice the gameplay deficiencies more as well and become overall less tolerant of annoyances or bad gacha luck. The only independent issue is that they've failed to figure out how to make the game less hostile to new users in a way which doesn't fuck existing players.