I think the criticism is fair as far as the early version of the game goes. I think now though it's more in line with what they had in mind. Here's how it is now.
The high end drops are more common. I got one by giving a citizen in need a bottle of water
Vendor system has been revamped to include high end blue prints for gear and weapons
Weekly and Daily HVT's added to the base game world for those who don't like the DZ or don't have the Underground
World Tier's added. The higher the tier the harder the enemies but the greater the rewards. This is spread across all aspects of the game.
Improved Gear Sets help cut down on TTK. So if I have all my armor pieces from the same set then I get huge bonuses applied to my avatar. They have a lot of different sets to suit players play styles. I have 3 different sets and I use each one for a different reason. One gear set helps offset Rogue Agents as in if killed by them I don't lose much of anything as far as gear looted goes and I gain 20% health against them as well as deal 20% extra damage to them. That's one example.
Improved Incursion(think Raids from Destiny) performance. Better drops, bug fixes, requirements to play lowered
Supply drops every hour in the DZ. These occur now in each zone, 1-6, as opposed to just one for the entire DZ map. They also occur now in the main map but not as often as in the DZ. Supply Drop gear does not have to be extracted from DZ.
Enemy level now scaled to the Group Leader's rank when doing the campaign. This helps big time in helping friends who are just now starting out.
These are just a few of the changes.
I think the TTK is fine because it can make a group of small bad guys feel like a large group. The engagements often require you to think as the AI is pretty good and will retreat, flank, take cover, etc etc. Plus you have to know what you are dealing with. If they have a medic you need to take them out or they can just keep healing and prolonging the fight. Guys with shields need to be flanked. Guys with flamethrowers don't suffer as much from fire effects. Big bosses can use EMP to disrupt your specials and can also be equipped with the same specials you have. So it all comes down to how your group handles it.
I think that having a shorter TTK or one shot one kill mechanics wold make the game worse because of the shear ease in which you would be able to dispatch them.It would force the game to flood the streets with NPC's in order to present any real world threat and that would take away from how the game feels.
A lot of it also depends on what you want from the game. If you want a challenge then there are ways to seek it out and find it but if you want to be more casual you can do that as well.
Now that's not to say it's a perfect game but it has come a looooooong way from the game it was at launch and has now found a sweet spot.
The one thing I really wish they would do is give players an option for a PvE or PvP Dark Zone. PvE your gear would stay the same and they enemies would stay the same or they could increase their numbers because you wouldn't have that Rogue Threat but you would still see other groups of agents on the streets and could help and assist. PvP all the gear should be normalized when you enter the server and special abilities should be nerfed or turned off.