It's a tough situation realistically. A faster TTK is generally caused by a good hit detection, but conversely slows the game down because being 'insta-killed' is far more common.
There is no way on this planet that the M27 from Black Ops 2 only kills .4 seconds slower than the R5 in this game. I'm sorry but that just isn't how it was after using both guns extensively. The M27 is probably the biggest hitmarker gun In the entire Call of Duty franchise whereas the R5 is anything but that, and certainly not the 2nd slowest killing assault rifle out of every single one listed there.
The lag compensation needs to be removed or corrected and dedicated servers desperately need to be mandatory in all online modes. This game certainly didn't help with the idiotic idea of removing the green/yellow/red ping bars which were a good indicator of who was host, who was living in Mexico and who was downloading something in the other room causing massive lag spikes.