Well most of people who come through H1B gets GC applied by same company who sponsored them and after certain time of GC those people can sponsor their family without issue just their work record is enough .

Usually people include their Employment status documents with sponsor letters otherwise credits checking is just formality for processing i doubt if they even do check it . Everything depends luck and nature of person who is applying . Young people who are trying to come through their relatives sponsor letter for certain time in visiting visa has very less chances to get Visa most of them are denied saying they will stay back in US and work .

F1's can sponsor their relatives for Graduation's only .