Bulk Renaming column in PQ with a pattern

I would try this way first, in a single rename columns step using List.Zip and List.Transform.

let
  src=Table.FromRows(
    Json.Document(
      Binary.Decompress(
        Binary.FromText("i45WMlTSUTICYmOlWJ1oJRMgyxSIzZRiYwE=", BinaryEncoding.Base64),
        Compression.Deflate
      )
    ),
    let
      _t = ((type nullable text) meta [Serialized.Text = true])
    in
      type table [#"db[colA]" = _t, #"db[colB]" = _t, #"db[colC]" = _t]
  ),
    #"Renamed Columns" = Table.RenameColumns(src,List.Zip({Table.ColumnNames(src), List.Transform(Table.ColumnNames(src), each Text.BetweenDelimiters(_, "[", "]"))}))
in
    #"Renamed Columns"

Pat

I have a custom function ShortenColumnNames that I run on all of these:

(Source as table) as table =>
let
    ColNamesList = Table.ColumnNames(Source),
    Transform = Table.RenameColumns(Source,
        List.Transform(ColNamesList, each {_, Text.BetweenDelimiters(_, "[", "]")}))
in
    Transform

 So each of my SSAS queries starts like this (I keep the DAX queries separately):

let
    Source = AnalysisServices.Database(Workspace, Dataset, [Query=DAXQuery, Implementation="2.0"]),
    RenameCols = ShortenColumnNames(Source),
    [...etc...]