New story content and occasional new characters are not what's lacking and they're never going to stimulate or reinvigorate a post-campaign playerbase to keep them coming back and start spending (which is the whole point of a service game).
The post-campaign game is terrible. It wants desperately to be a Destiny or Division, but simply lacks anything resembling a fun sandbox/open world that's enjoyable to be out and about doing things in (even vs Destiny's limited destinations of semi-open areas linked by tunnels and corridors, that out-does this game's menu-driven cramped and limited destinations handily). Even Anthem had it beat for that. The vareity of missions in nonexistent. Destiny has Patrols, Lost Sectors, Strikes, Raids, Exotic Quests, various PvP modes, a PvEvP mode and more besides... Marvel's Avengers has the same old stuff in various boxes with different labels. The approach to invisible loot and paid/earned skins was a good attempt in some regards, but feels utterly hollow as a player. The combat itself is good to great depending on the character you're playing, but the scenarios and destinations are limited, checklist and repetitive.
They can add characters X, Y and Z every month for a year and all it'll result in is a small wave of people dipping in and out just as quickly; it would interest some but it's not the kind of userbase cultivation that's required to get people in or keep them invested and prompt their spending.
3 months on, 12 months on, it makes no difference unless the fundamentals of the post-campaign change drastically. It's not too soon to call it. The game in its current form is dead and can't be reanimated with just more of the same. That's why this game is dead now and will remain so until they pull the plug on the servers without a hefty rethink.
