Hi! のんびりしています in this sentence doesn't indicate a progressive action. The ～ている form can also be used to indicate a particular state or condition. Examples: 1. 瘦せる "to get thin"　→　瘦せている "to be thin" 2. 乗る "ride or take (a bus, a car, etc.)" →　乗っている "be in a bus, car, etc." 3. 眼鏡をかける "to wear glasses" →　眼鏡をかけている "be wearing glasses" Therefore, regarding のんびりしています in your sentence, it means "to be more easygoing" You can't use します in ジョンはデレクよりのんびりします。to express the same statement. I believe that ツンデレ colloquially indicates a chill, cold or aloof personality. Hope that helps.