The success rate of NFL drafted players varies significantly by position. It should be clarified that debating whether a player's career is considered "successful" can be subjective and depends on many variables including, but not limited to, team situation, health and fitness level, etc. However, based on your definition, players who start for at least 5 seasons, here are some rough estimates based on available data:
1. Quarterbacks (QB): Historically, it's known to be risky to draft quarterbacks. According to a 2017 study by the Harvard Sports Analysis Collective, about 35% of first-round QBs turned into top-level starters, while the rate drops drastically to around 10% and 2% in the second and third rounds respectively.
2. Running Backs (RB): A study by Cade Massey and Richard Thaler showed that about 33% of first-round RBs become successful. The success rate in later rounds reduces considerably.
3. Wide Receivers (WR): The same study suggests about 64% of the first-round WRs can be classified as successful, while the number drops significantly in the later rounds.
4. Offensive Line (OL): These positions like Guard, Tackle, Center tend to have steady production over time and can be very successful. Historically, approximately 60% of OL drafted in the first round fall under the given definition of success.
5. Tight Ends (TE): Though reliable data isn't readily available, various sources cite that roughly 30%-40% of TE drafted in the first round are successful.
6. Defensive positions (DL, LB, CB/S): Defensive Linemen see around a 66% success rate (Massey-Thaler). Linebackers have a success rate of 56% in the first round and significantly less in subsequent rounds. Lastly, first-round cornerbacks/safeties have a success rate around 61%.
Keep in mind these percentages can fluctuate in different draft classes and depending on how "success" is defined. Current player development practices, coaching, and advances in injury prevention/treatments can also affect these figures.