Remove Windows Defender from default install
1) Windows Defender causes the installation of a lab setup to be 4x slower: https://github.com/Microsoft/ws2016lab/wiki
2) Please don't even get me started on how wrong you are doing if you need to put an antivirus solution IN A SERVER. (WTF Microsoft?!)
3) Obligatory xkcd reference: https://xkcd.com/463/
Hi. Defender automatically excludes Hyper-V files and processing - https://technet.microsoft.com/en-us/library/dn913616.aspx - what part of the lab setup becomes slower, specifically? It's possible an exclusion was missed or a regression occurred in TP5, or you are talking about an unexcluded operation. It's not going to be removed, so we need to understand problems.
There is nothing strange or bad about servers running 3rd party security software, that has been a best practice for decades. We and third parties have made such software before (SCEP, FFA were ours).
* All Nano Server packages of TP5 = 216 MB.
* Largest package = 124 MB.(Windows Defender)
* Second largest package: 26MB (OEM Drivers)
* All packages WITHOUT Windows Defender: 92MB