There is, in fact, progression in the game. The problem? It's pretty deep in.
See early on most items have single stats. For example most items follow the following formula:
Green = 1 base modifier (1.15x crit dmg, or 1.10x magazine, or 1.15x melee dmg, etc)
Blue = 1 base modifier, sometimes a Synergy
Purple = 1 base modifier, 1 special modifier (15% grenade recharge on kill, 10% ego refresh on critical kill, etc), Synergy
Orange = 1-2 base modifiers (sometimes stronger such as a 1.25x crit dmg), 1 special modifier, Synergy
Now those are the basic stats on most of the weapons right out the game. It follows these trends pretty good with the only real noticeable thing as you level is full Synergies become more common.
HOWEVER...around 1600 that's when another progression tick comes into play. That's when you start to see basic level weapons get better and stronger. You start to see things such as basic greens having two set bonuses that are also stronger like an Orange:
http://steamcommunity.com/sharedfile.../?id=139277536
Note the way that Assault Rifle has a 1.25x modifier instead of just a 1.15x modifier. You also see Blues with full Synergies and again the dual bonuses:
http://steamcommunity.com/sharedfile.../?id=139277346
(note that's
+40% melee damage...)
This means you can have greens with stronger base modifiers than Oranges. Think of it like this:
Another thing you'll notice is these weapons don't have all their mod slots. Likely what this means is as things ramp up towards 1500 (around 750? 1000?) weapons get all their mod slots and then lose them when they tick into the next bracket of power scaling. Over time I imagine you will see more mod slots in the bracket as you work towards the next bracket (which would make sense if it was around 3000-3200 or so because that'd give a place for a final bracket around 4500-4700 leading to 5000).
So the real problem isn't that there isn't progression, it's that progression takes such a long time that your average player won't notice it for quite some time. I mean really once you hit around 1250 and have done most of the pursuits (or grinded a lot) things slow down quite a bit as Major Arkfalls become your only real source of XP. That means your average person won't be hitting 1600 for a while (since honestly it REALLY slows down 1400-1500+) which means they likely won't start to see these bonuses kicking in.