C# Functional MergeSort

FunctionalMergeSort.cs

public class Functional
{
    public int[] MergeSort(int[] array)
    {
        if (array.Length < 2)
            return array;

        var (arrayA, arrayB) = Split(array);
        var sortedA = MergeSort(arrayA);
        var sortedB = MergeSort(arrayB);
        var mergedArray = Merge(sortedA, sortedB);
        return mergedArray;
    }

    private (int[] arrayA, int[] arrayB) Split(int[] array)
    {
        var arrayA = array
            .Take(array.Length / 2)
            .ToArray();
        var arrayB = array
            .Skip(array.Length / 2)
            .ToArray();
        return (arrayA, arrayB);
    }

    private int[] Merge(int[] sortedA, int[] sortedB)
    {
        return Enumerable.Range(0, sortedA.Length + sortedB.Length)
            .Aggregate(
                seed: new
                {
                    arrayA = sortedA as IEnumerable<int>,
                    arrayB = sortedB as IEnumerable<int>,
                    merged = new List<int>() as IEnumerable<int>,
                },
                (aggr, _) => (aggr.arrayA, aggr.arrayB) switch
                {
                    var (arrayA, arrayB) when (arrayA.Any() && !arrayB.Any()) ||
                                              (arrayA.Any() && arrayB.Any() && arrayA.First() <= arrayB.First())
                        => new
                        {
                            arrayA = aggr.arrayA.Skip(1),
                            aggr.arrayB,
                            merged = aggr.merged.Append(arrayA.First()),
                        },
                    var (arrayA, arrayB) when (!arrayA.Any() && arrayB.Any()) ||
                                              (arrayA.Any() && arrayB.Any() && arrayA.First() > arrayB.First())
                        => new
                        {
                            aggr.arrayA,
                            arrayB = aggr.arrayB.Skip(1),
                            merged = aggr.merged.Append(arrayB.First()),
                        },
                })
            .merged
            .ToArray();
    }
}