Botham hit a purple patch in the first 2-3 years of his career. After that, he was just pretty ordinary. His bowling average was close to 40 after the early 80s, inspite of playing many home matches on friendly wickets. Kapil was a lot more consistent inspite of taking on a much bigger burden - Kapil played far too many matches, played without decent support bowlers at the other end, bowled 70% of his career on unfriendly Asiatic conditions and so forth, and also lifted his game against WI - even producing a 9-83 against a beastly WI side on an Indian wicket. (though it could not win the match - but what more can a bowler do?)
Kapil has some of the best knocks in the WI at their prime. Kapil is the only batsman in history to hit a run a ball 100 against a WI side that included all four - Marshall, Roberts, Garner and Holding. Kapil hit the two most brutal fifties against the WI at their peak in their own backyard. See for yourself.