I use Yahoo! but haven't noticed those recent changes. I've been using Firefox browser plugins to hide the ads and the crufty right column junk for so long that I forgot it was there until I opened it in Chrome on a borrowed laptop.
One thing that you can do to get rid of all the junk is to disable JavaScript on Yahoo! mail (there are a number of ways to do it) and it will revert to the old school Classic interface.
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An easy way to block Javascript on Yahoo! mail is to use a plugin like UBlock Origin and click the script button like this when on the Yahoo! mail page:
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