Yeah i agree that the quality backlinks is always work but in case of directories, it is different. If you have realized that if you submit your site on Directories sites, after approval have you checked Google Console links to your site?
If you see you would realized that you have submitted only one url on that directory but there would be more that one backlink coming from that particular directory.
If it came from a quality directory then more than a link from that directory just benefit for your site, no worries on that.
For example when I have 300 links in 300 posts from signature on a quality forum but in my Google Console links to your site its showing 700 links from that site, I don't know how Google calculated that but its beneift for my keyword ranking. I tried to move the signature then my keyword rankings decreased.
Its reason why I said you don't need to worry about number of links on a quality site.
By directories if you mean something crap then I would say it's no more than wasting time and efforts. However, when it comes to authoritative sites then surely directories have importance in a way that it can bring traffic to your site and this traffic eventually results in generating some leads.
So directories are important but having niche relevant directories. For example if you have website of leather jackets and you are submitting it in the directories of science then it's better to play some video games rather than spending that time.
Directories probably do not work as well as the Yahoo directory did back in the good ole days. You still get a backlink though. It seems to be a little difficult finding regular directories any more, perhaps that is just me.
In 2018 directory submission is an old method, but this method was really helpful to create backlinks. Maybe paid version of it can be work. On these days guest posting, web2.0, bookmarking is works great.
Why it wouldn't work?
Just because some people who have nothing better to do but to blabber
about thing they don't really understand in posts they are making just to
post counting doesn't mean something is broken.
Myth about directories started when there was 20,000 dead on arrival
directories would start and die every month and when submitting would be
waste of time, than granted, buy bother but now directories in many cases
are source of link, something no one should ignore.
In 2018, Directory submission is like a dead part for SEO. It's totally a time wasting technique, I think content sharing through social media will give you a better result more than directory submission.