The result of some boredom.

TT2MasterGSImport.js

//Imports tt2master small export string
//Change variables according to your locations
function tt2MasterImport() {
  
  var sheetname = "Input"; //sheet name for input
  var artRow = 2;          //starting row for artifact input
  var artKeyCol = 1;       //column for artifact key
  var artValCol = 2;       //column for artifact value 
  var spRow = 2;           //starting row for skill input
  var spKeyCol = 3;        //column for skill key
  var spValCol = 4;        //column for skill value
   
  var doc = SpreadsheetApp.getActiveSpreadsheet();
  var temp = doc.getSheetByName(sheetname);  
  
  //make sure that the input sheet exists
  if (!doc.getSheetByName(sheetname)){
    var sheet = doc.insertSheet(sheetname);
  } else {
    var sheet = doc.getSheetByName(sheetname);
    //clear old data
    sheet.getRange(2, 1, sheet.getLastRow(), sheet.getMaxColumns()).clear({contentsOnly:true});
  } 
  
  //get json
  var rawjson = doc.getSheetByName("Input").getRange(1, 1).getDisplayValue();
  
  //parse json
  var dataAll = JSON.parse(rawjson);
  
  //get artifact data
  var artData = dataAll._artLvls;
 
 //output artifact data
  for(var i=0;i < artData.length; i++){
    
    var keyRange = sheet.getRange(artRow, artKeyCol)
    keyRange.setValue(artData[i].ID);
    
    var valRange = sheet.getRange(artRow, artValCol);
    valRange.setValue(artData[i].Level);
    artRow++;
  }
  
  //get skill data
  var spData = dataAll._skillLvls;
 
  //output skill data
  for(var i=0;i < spData.length; i++){
    
    var keyRange = sheet.getRange(spRow, spKeyCol)
    keyRange.setValue(spData[i].TalentID);
    
    var valRange = sheet.getRange(spRow, spValCol);
    valRange.setValue(spData[i].CurrentLevel);
    spRow++;
  }
  
  //for output
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  ss.toast("Done. Inserted "+(artData.length + spData.length)  +" items");
}