Kirby is more consistent and its highs are mostly thematic due to most of its content being intentionally very easy and simple until the late-postgame in nearly every title. Mario's highs are gameplay-oriented and are very high in that regard but it has more lows than Kirby by both volume and the sheer quality drops of those low points. Kirby isn't devoid of bad games but most of them are spinoffs while the only mainline Kirby I'd say is outright weak is DL2 (though I won't argue anybody saying Star Allies).