How to equate array variables to other array variables in a formula

As seen in Example, I'm trying to convert FTNA to FTVA. They are the exact same size, but I am only trying to get the text within the brackets of FTNA. However, whenever I do this, all I get is "This is invalid". Can anyone tell me why?

Sub Example()
Dim mcfc As Worksheet
Dim FCMC As Long
Dim FTVA As Variant
Dim FTNA As Variant
Dim i As Long

Set mcfc = Workbooks("PERSONAL.xlsb").Worksheets("Sheet1")
 
FCMC = mcfc.Cells(1, Columns.Count).End(xlToLeft).Column

FTNA = WorksheetFunction.Application.Transpose(WorksheetFunction.Application.Transpose(Range(mcfc.Cells(1, 1), mcfc.Cells(1, FCMC))))

    For i = 1 To FCMC
        FTVA(i) = Mid(" & FTNA(i) & ", InStr(" & FTNA(i) & ", "(") + 1, InStr(" & FTNA(i) & ", ")") - InStr(" & FTNA(i) & ", "(") - 1)
    Next i

End Sub