I have seen a lot of posts talking about INS:S's Time-To-Kill, and I have to agree to the fullest. I am an advit player of both INS and DOI with the combined play time of around 700hrs (INS takes up the majority of play time), and I love both of those games because of it's super fast TTK, especially in INS with the addition of light and heavy armor compared with DOI.
After playing around 30hrs in INS:S (both Co-Op & P.V.P.), the TTK is night and day; I find myself emptying magazines faster than before just for two, OR ONE, enemy, and I'm talking about enemies from medium range. From a few posts I've read, I confirmed my own personal belief that the TTK is similar to the recent Battlefield games; I knew that the gunplay felt familiar somehow. I've favored the M4A1 for most of my loadouts, and the TTK with the most expensive assault rifle feels like the M16A3 from BF3 (both shoot fast, but still needs a significant amount of bullets to take down one guy).
I don't know whether or not if input lag, hit detection, hitboxes, internet lag, or whatever is affecting the TTK in some critical way. The game is still in BETA, and the developers have been updating the game in bulk, so there is a chance that the game being in BETA has been affecting the game negatively in a way that the developers doesn't intend to. I've read thoughtful past posts that point out that heavy armor may be the problem with the TTK and that the absence of AP rounds is the reason why it takes so long to take down an enemy. For a number of players, including me, the return of AP rounds is a definite no since it'll be another case of the Stopping Power perk from COD, so there must be some way to combat against the long TTK. I myself love the NWI's work because of how quick the TTK is, staightfoward and concise.
So I believe my suggestion from the title is a good compromise to combat against the TTK and the heavy armor problem without introducing AP rounds again: either increase both Damage & Penetration for all Weapons or Lower Health & Armor Defense to Combat Current TTK. I realize that this game is being marketed for a wider audience, so there are slightly new gameplay elements based off of INS that are turned into something more casual-like, but as a long-time player of both NWI's work, I loved both games for its quick TTK. I wasn't much of a hardcore FPS player before INS, and ever since then, I never turned back for the cliche FPS games I used to play.