I think the real test of the games longevity will be when it starts a new season. I'm not even sure if they know how they will truly implement it yet, and it's only a few weeks out if they keep the 6 week schedule.
Cohhcarnage recently had a talk with the devs, had to have a translator for it too, where the end conclusion was basically that they knew that the faster paced seasons would filter out some players and it seems like they are focusing on the more hardcore crowd so to speak, not the casuals who have limited amount of playtime.
So how that will translate to earnings for the game over time is .... questionable? You focus on hardcore. They consume content fast. Can you keep up with making "new" content every 6 weeks to satisfy a hardcore audience? The hardcore players hit the cap on the phases 1-2 days after they were released. What will a new season deliver? They're going to have 8 seasons per year?
And how will they be able to monetize it over time? As others have mentioned here, it's a very well done free to play system, not pay to win, but you can easily consume what is there without making any purchase. Take Path of Exile as an example, it's free to play, but how long did you play it without spending at least some money on the tabs? Once Human has none of that. Some here have spent money because they felt it was deserved of the game, not because it gave any real benefit at all in the game.
It's certainly not a bad game, but as a live service game that needs constant updates and servers up, I'm not sure if the monetization is there to keep up development costs. Especially if they purposefully plan to cater to non-casuals and limit their customers to such a degree.