It's difficult to even do that based on the number of years a particular driver has/had been racing. IOW, you can't compare Jeff Gordon to Kyle Larson.
If you want to talk about win percentage based on number of races won then Herb Thomas kicks all their asses.
- Overall all-time winning percentage: [drivers with over 100 starts]:
1. Herb Thomas -- 21.053% (48 wins, 228 starts)
2. Tim Flock -- 20.856% (39/187)
3. David Pearson -- 18.293% (105/574)
4. Richard Petty -- 16.892% (200/1184)
5. Fred Lorenzen -- 16.456% (26/158)
6. Fireball Roberts -- 16.019% (33/206)
7. Junior Johnson -- 15.974% (50/313)
8. Cale Yarborough -- 14.821% (83/560)
9. Jimmie Johnson -- 14.498% (78/538)
10. Ned Jarrett -- 14.205% (50/352)
11. Dick Hutcherson -- 13.592% (14/103)
12. Lee Petty -- 12.646% (54/427)
13. Fonty Flock -- 12.338%(19/154)
14. Rex White -- 12.047% (28/233)
15. Bobby Issac -- 12.013% (37/308)
16. Bobby Allison -- 11.699% (84/718)
17. Jeff Gordon -- 11.567% (93/804)
18. Dale Earnhardt -- 11.243% (76/676)
19. Joe Weatherly -- 10.890 (25/230)
20. Darrell Waltrip -- 10.383% (84/809)
(stats from Racing-reference.info and NASCAR Statistics and compiled weekly here)(10-16-2016)
Jimmie Johnson being in the top 10 of that list is very impressive considering no one else who was a regular winner since the 1980s is.