> FTP has mget
Not quite, ftp CLIENTS have mget. The ftp protocol has absolutely no awareness of mget. In fact, ftp is terrible at downloading more than one file at a time because it has no concept of pipelining and keepalive, both things that http supports.
With a nice multi protocol client like lftp, http directory indexes work just like an ftp server:
$ lftp http://http.debian.net/debian/
cd: received redirection to `http://cdn-fastly.deb.debian.org/debian/'
cd ok, cwd=/debian
lftp cdn-fastly.deb.debian.org:/debian> ls
drwxr-xr-x -- /
-rw-r--r-- 1.0K 2017-01-14 10:44 README
-rw-r--r-- 1.3K 2010-06-26 09:52 README.CD-manufacture
-rw-r--r-- 2.5K 2017-01-14 10:44 README.html
-rw-r--r-- 291 2017-03-04 20:08 README.mirrors.html
-rw-r--r-- 86 2017-03-04 20:08 README.mirrors.txt
..[snip]..
lftp cdn-fastly.deb.debian.org:/debian> mget README*
5315 bytes transferred
Total 5 files transferred
lftp cdn-fastly.deb.debian.org:/debian>