To be fair to him, the win or loss is derived from skill though but I take your point all the same.
Basil,
It sounds like you may have played a relatively few amount of games for it to "kick in" properly. The 5 placement games is a very low sample size for Treyarch to measure your ability but we all have to acknowledge that they have to get the ball rolling.
If thats not the case and youve played 50+ games in total on league play then something of the following is happening:
1) You're regularly playing in a party that have players better then you
2) You're having incredibly good fortune with your random team mates (this is unlikley over say 50 games though.)
3) You're adding more of a contribution to a teams win they you currently believe so.
Its very possible a combination of these are happening too but dont overlook number 3. Its very possible for a "better player" to out perform you in a particular battle but only in detriment to his own teams chances of winning (less value kill, messing up a spawn, ignoring objective, disregarding more pressing things to do etc.)
Its entirely possible (although not necessarily desirable) in some circumstances to go 17-24 and be more of an asset to your team then the opposition player who goes 31-14 is for his own team. From the sounds of it, for whatever reason, what cant be denied from the looks of it is.... you're winning games more often then losing. Just need to figure out why.
Although its difficult to get your head round it by the way, right now, you are definitely improving. Playing against better players is the best way to do this and from the sounds of it, this is what you're doing. If you want to get better, keep playing.