Team xG doesn't allow for differences in the quality of those attempting the shots or those in goals, therefore it is only useful when used in tandem with other metrics, like individual player xG and a reliable player rating system.
To assume a team was lucky or unlucky based purely on team xG...
Looking at last seasons premier league player xG stats, Josh King at Bournemouth scored highly. Looks good on paper and from what I saw in the cup match, he would definitely be a player I would be happy for us to target.
As for the xG ranking teams, there doesn't appear to be a clear pattern...