SharePoint folder "modified" date not accurate

I've just had a very fraught call from a client after a big migration of their entire SharePoint system from sites to groups. They were panicking that the migration had failed. I know it hasn't as I'd written a PowerShell script that listed EVERY single file in the source and checked everyone single one existed in the target with the correct timestamp (can't compare sizes as OneDrive/SharePoint still adds metadata on upload).

In the end, I placated them by installing the FolderTimeUpdate utility on the PC and getting it to update the folder times of their synchronised copy.

BTW - the fact this tool exists shows that even Windows doesn't always get the folder dates right!

But it shouldn't have to exists and neither should it on SharePoint. It is IMO a relatively simple task to do what FolderTimeUpdate does for Windows. A relatively simple background script can scan through every file and ripple the modified date back up the parent tree.