Blastman,
We are using the same definitions then regarding lag shooting... Talking about needing to compensate for network lag. Some previous posters appeared to be defining lag shooting to mean what you are calling "lead shooting". That is, needing to compensate for a weapon's travel time, target velocity, etc.
MW4 definitely had travel time weapons, that were not instant hit. As pointed out, folks like MekTek modified the travel time of the weapons later in MW4's life cycle to speed up some of the travel time weapons in an attempt to make them more competitive. To folks who thought all the weapons were instant hit (not you), I'm not sure what to tell them.
Regarding lag shooting, unless you always played on a LAN, network latency had a non-trivial impact on the game. The major reason for this, I believe, was that prior to PR1, hit detection was all done clientside. If you saw a hit on your screen, then it was a hit on the server, and the damage got propagated to the target (regardless of whether or not THEY saw the hit).
However, PR1 moved the hit detection off of the client and onto the server, in an attempt to combat certain hacks that had emerged. However, when they did this, what you ended up having was a game whose netcode wasn't really designed for the task at hand.
This isn't really an opinion. This is simply a statement of fact. If you would like proof, please go to
MW4's original site (which I am, frankly, amazed is still served up my Microsoft). Now, bear in mind that at the end of Vengeance's lifecyle, you can't get to the original PR1 patch. However, what you can see from that link is the readme file for the 3rd patch release for vengeance. In those notes you see:
Quote
The patches fix several instances of a bug that caused certain ’Mechs using Jump Jets to be significantly more difficult to hit than other ’Mechs.
The patches fix a bug that sometimes resulted in damage not being recorded correctly in multiplayer games. This behavior still appears occasionally as the result of games with high server lag, but the patches should reduce the instances of the problem significantly.
The reality is, they were never able to fully fix the bug, due to inherent deficiencies in the netcode that was designed for clientside hit detection.
Oh, also, our unit actually worked with the devs directly to help identify the bugs with damage being dropped.
At this point though, if we're still in disagreement, we'll just have to agree to disagree.

It's no big deal anyhow, whether or not there was lag in a game over a decade old at this point.