Teams can be blamed at times, but it cant possibly be everytime. The players at a + have gotten their not because of luck. Although i will say getting out of the B range is tougher than climbing the A ranks as there are more competent teammates in the higher ranks. The best and only way to overcome this imo is by focusing how u can make your team better and fixing whatever errors you make (no matter how small they may be) and be able to accept the fact that you will play in a bad team again.