In my opinion the invitation system is both fundamentally flawed and counter productive to the game (and company) itself. The system rewards people for inviting players that have not spent any money and since the reward drastically aids both players, why would they buy the rest of the game? That means Mercury Steam gains few to no sales on invited players. Additionally, in order to adequately find people to invite, the player must use services outside the game itself (such as discord, forums, steam chat groups, etc.) since there is no in-game communication available. This creates a barrier to entry for the "feature" and thus limits it's effectiveness at increasing the player base. Not to mention the hit the company is taking on player opinion/satisfaction based on how difficult it is to unlock things without the invitation system; which again damages the chances for future sales to those dissatisfied players (or their friends).
I'm sure the system was conceived with good intentions but to me it doesn't seem like the positives out weigh the negatives. Sure, there is a group of players that take advantage of the system but the long-term damage the system itself is doing seems too dangerous to keep around. I'd personally aim to smooth-out the player progression experience and work to foster positive player experiences that they would want to share with their friends (thus bringing in more paying players).
But that's just my take on the situation.
This sums the situation pretty well.
In bold, the critical aspect of this situation:
satisfaction. Lately I have been playing Raiders without feeling any rewards from the game.
These are my days in Raiders: I wait long qeues with my couple (she started to play 4 days ago); we play with people who just skyrockets the difficulty score with their levels (and levels adquired by buying things...it's unfair), or, people who can't get along with the team (lacking an ingame chat to just give advice or something HURTS this game A LOT). In the end we can't even feel any satisfaction when we win; it has become more than a challenge, it's a constant beating to just get nothing.
To be honest, we have faith in some kind of co-op with bots, difficulty level selector...We just want to enjoy the game at our own pace. We have been doing with every other game in the market, why this one neglects that so hard?
I'm afraid; I asked about some changes and they told me that they were on them; hours later I get H.I.V.E. and the same history as Ginebra, Iune and Mikah... It's frustrating to just want to get all the experience and knowing it can't be.
I tried to get more people into this (only succeeded with one person) but everyone in my friend's list says the same: "Man, the game is...too grindy; I can't get into that because is too bad; I'm not playing that is just a pay to play but with free to play mechanics; This is like Battlefront 2.".
I give up. I enjoyed the game these months but I give up.
If I want the other campaigns I just need to ask anyone to invite me, it's easier, cheaper, and I can see the story.