Maybe helpful: When switching between samba and ksmbd, or when updating an smb server, it is sensible to clear Windows' Kerberos ticket cache. Keeping the Kerberos tickets but changing the server they relate to can lead to strange side effects.
Open an command prompt as administrator and issue klist purge
What you have is the current "minimal" samba4 server installation and outside from switching to ksmbd or using a extroot there is nothing else you can do.
The main issue is that starting with samba4 the build system was changed and all the old 3.6 hacks to trim down the server size do not work anymore.
Sure on a windows only setup you can remove Avahi daemon/bins, but you still need the avahi-lib since samba is compiled against it. The bulk size is in the samba-lib package anyway, which cant be reduced.
Well it seems that any other Windows user profile I use (not being my current profile) within Windows 8.1 / 10, works with ksmbd.
I tried removing any current remote connections of my current profile by using the commands: net use * /d ....then followed by.... klist purge ....however it's not making any difference.
EDIT: the only way I gotksmbdto work using my current Windows profile, was to change the share-name
I gather the old Samba4 share-name that I previously used, is somehow still utilized within Windows and clashes with the ksmbd installation?
Nevertheless, early days using ksmbd, happy that I have now reclaimed 12MB of free package space!