I was interested in this as well, so I had a look, this is what I found (Long answer) -
Windows Defender Advanced Threat Protection (ATP) uses the built-inWindows Defender Antivirus, which can be used as the primary antimalware product on your endpoints. In fact, Microsoft says they workbetter together. If using a third-party antimalware client likeESET, Windows Defender Antivirus on that endpoint will enter into passive mode.
So you could already replace ESET with Windows Defender, now part of Windows Defender Security Center app,if you feel it offers suitableprotection. Windows Defender ATP is completely optional and you would have weigh up the value of its breach detection, remediation and response featuresin your environment and with the costs involved ofWindows 10 Enterprise E5/Education E5 orSecure Productive Enterprise E5. I'd start with a demo or trial and better understand its features perhaps.
Office 365 ATP is advanced email protection that goes far beyond what the built-in Exchange Online Protection provides.
Also, there is Advanced Security Management in Office 365, which is another thing to look into. Both this and Office 365 ATP are included in Office 365 E5. Have a look at this presentation if you get a chance - Deep Dive - Office 365 E5 Security Capabilities.
So the short answeris it depends! It up to you to decide what is suitable and whether your security stance is strong enough and budget, of course, is a factor. Perhaps have a look at Office 365 Secure Score first and see if there areimprovements you couldmake already to bolster your security posture. Hope that helps a bit anyway.
