Saving charts as images when converting xls to Google Sheets - Google Script - google-apps-script

Question

I have a standard script from the Internet which converts xls to Google Sheets. The charts in the output file got converted to images which is a good thing, I needed charts to be saved as images as the original xls have specific formatting I would like to preserve but the problem is that they look awful - the color shaded, the font dropped to a very small size, the legend floats somewhere. Ultimately I need to have these images to be saved in Google Slides. So, what I was thinking is to find a way (1) to save images from xls and saves directly in Google slides or (2) to save images from xls to Google Sheets but somehow preserve the original formatting and then, run another code that saves the images to the target Slides. Interestingly, I have not found any mention of people complaining of the loss of the chart formatting.
function convertExceltoGoogleSpreadsheet2(fileName) {
try {
fileName = fileName || "name";
var excelFile = DriveApp.getFilesByName(fileName).next();
var fileId = excelFile.getId();
var folderId = Drive.Files.get(fileId).parents[0].id;
var blob = excelFile.getBlob();
var resource = {
title: excelFile.getName().replace(/.xlsx?/, ""),
key: fileId,
parents: [{id: 'id'}]
};
Drive.Files.insert(resource, blob, {
convert: true
});
} catch (f) {
Logger.log(f.toString());
}
}