Gillespie played 10-11 years of international cricket.
71 matches, 137 innings,
259 wickets at 26.14 , ER 2.85
54.96 SR, 0 x 10 wickets, 8 x 5 wickets
1979-89
Kapil Dev
97 tests, 163 innings
346 wickets at 28.13, ER 2.85
59 SR, 2 x10 wickets, 21 x 5 wickets
Similar SR and ER
Kapil far better WPI, 5fers and 10fers
Gillespie avg better by 2 points. For that, he needed better conditions, better bowling support , better fielding support and score board pressure.
Kapil is arguably better than Gillespie and no way they are in different leagues as bowlers.