You can't completely judge someone's ability based on their K/D, but it is a good indicator. It is true, a lot of players with the top K/D's (3.0+) inflate theirs by always playing with a team, staying back, taking no risks, but at the same time not making any plays. Those teams would often lose against a team of ~2.0 K/D's who actually play actively, flank, work together etc. Often times though, someone with a K/D of 2.0 will be far superior at least in terms of gunskill to someone with a 1.0.