DNS works with host, but not with wget

This is the first time to see resolve hosts keyword, it seems wrong. You should have something like

hosts: files dns [NOTFOUND=return]

or if you have mDNS installed

hosts: files dns mdns4_minimal [NOTFOUND=return] mdns4

You can remove [NOTFOUND=return] or [!UNAVAIL=return] , it's the default action anyway if nothing left to query.

Well, after some digging I could find that there is an NSS module new to me

libnss-resolve

nss module to resolve names via systemd-resolved

nss-resolve is a plugin for the GNU Name Service Switch (NSS) functionality
of the GNU C Library (glibc) providing DNS and LLMNR resolution to programs via
the systemd-resolved daemon (provided in the systemd package).

Installing this package automatically adds resolve to /etc/nsswitch.conf.

You could end up installing it somehow and not with the packages you mentioned. There is no package depends on it.

~$ apt-cache rdepends libnss-resolve
libnss-resolve
Reverse Depends:

But I can't say anything right now, why systemd-resolved was unreliable. It is better to report it as bug in systemd.