Because they were all running ARs with sharpshooter 5 going easy mode with keyboard and mouse. I was a heavy in chromosome using DS3 for the first few months and remember it was terrible unbalanced until I switched to mouse. I remember it was mandatory to have level 5 sharpshooter to be viable.
Played heavy myself. As I remember most was using ARs in Chromosome, there was very few logi as everyone with 2 equipment slots managed fine without the logi. Today we at least have the AR crowd divided between the scrambler rifle and AR for variety. I see less lasers, and less HMGs now but I see more forge guns and shotguns. I see a descent mix of logi and assault medium frames and about the same amount of scouts as previously. The sidearm is very underrated.

This is changing, I reckon. Between the vehicle rebalance and the huge buff to repair tools, logibroing has never been more profitable and I don't even have to kill a single soul to get to the top of the leaderboard sometimes. If people simply choose to slay over all else, then good. Slayers should be mainstream. If everyone ran logibro, then no one does the killing.

There's certainly lack of innovative roles but I would not call it mindlessness, I would call it the tendency for people to fall back on what they're comfortable with. And in an FPS, that's shooting other people with an assault rifle. Mindlessness is more like people banging their heads on a wall without stopping to try break through when there is a door next to them. The assault works, it isn't a complete waste of time and is beneficial to the team so it takes some degree of logic and intelligence to make the decision to kill people.

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The only decision CCP has to make is about how many new dropsuits they want to introduce. After all the racial variants missing, plus pilot suits, what's next? How much further is it envisaged to expand? Unique pilot suits for each vehicle type? Pirate faction dropsuits? Specialisations of specialisations (like say variants of assault suits with different suit bonuses)?

The further they expand, the less clearly roles will be defined by the game and more by the players in their innovation. If they choose not to expand dropsuits and instead focus on modules, same thing, more variation with modules.

Roles in Chromosome were defined because there was so little to choose from, and the massive drop of new dropsuits and weapons in Uprising changed that. As more and more content comes in, roles will be less and less clear to a beginning player, and I reckon that's cooler than having everything defined for you.

Remember how people would sh*t their pants when they heard a shotgun behind them?
Those were the days ...