假象，为什么遍历次数多反而耗时少？

《编程竞赛 - 数组父子关系的转换（完成）》
《坠入莱茵河@编程竞赛 - 数组父子关系的转换》

let array = [
    ['1', '', 'title1', 1, 2, 3],
    ['2', '', 'title2', 4, 5, 6],
    ['11', '1', 'title3', 7, 8, 9],
    ['21', '2', 'title4', 10, 11, 12],
    ['22', '2', 'title5', 13, 14, 15],
    ['111', '11', 'title6', 16, 17, 18],
    ['211', '21', 'title7', 19, 20, 21],
    ['2111', '211', 'title8', 22, 23, 24]
];

class ParseArray {
    constructor(inputArray) {
        this.inputArray = inputArray
        this.outputArray = [{
            "sub_data": []
        }]
        this.loopLength = 0
    }
    loop(pId, items) {
        this.inputArray.forEach((item, idx) => {
            this.loopLength++
                if (item[1] === pId) {
                    items.push({
                        main_data: item.slice(2),
                        sub_data: []
                    })
                    delete this.inputArray[idx] // 录入后删掉该条数据 可降低循环次数
                    this.loop(item[0], items[items.length - 1].sub_data)
                }
        })
    }
}

console.time("loop")
let val = new ParseArray(array.slice())
val.loop('', val.outputArray[0].sub_data)
console.log(JSON.stringify(val.outputArray))
console.log(val.loopLength) // => 26
console.timeEnd("loop")     // => loop: 0.2919921875ms

function convert_table_data_with_level(data, parent_node = "") {
    var level_1_data = [],
        new_data = [];
    for (var i = 0, len = data.length; i < len; i++) {
        data[i][1] === parent_node ? level_1_data.push(data[i]) : new_data.push(data[i]);
        recursionLength++;
    }

    return level_1_data.map(function(arr) {
        parent_node = arr[0];
        return {
            main_data: arr.splice(2, arr.length - 2),
            sub_data: convert_table_data_with_level(new_data, parent_node)
        }
    });
}

console.time("recursion")
let recursionLength = 0;
let data_with_level = convert_table_data_with_level(array, '')
console.log(JSON.stringify(data_with_level))
console.log(recursionLength) // 42
console.timeEnd("recursion") // => recursion: 0.098876953125ms