WP comes with a total package with all the rings and bells.
WB is a barebone backend which needs hardcore coding from the developer in order to create a website.
(forget the ancient templates and old addons, that stuff should be removed years ago and not be mentioned again )
And it's not what both systems can or cannot do, it's what yóu prefer as a commercial developer towards your customers. What do you reálly think it's best for them and their company.
Hm... I see it differently. WP doesn't come with bells and whistles. It's pretty barebone in its default form. You can create pages and blogs, that's about it. With WB you can create pages and news and forms. So pretty similar, although WB lacks a blog function, and its news moduel is very basic compared to the blog function of WP.
However, both are systems that let non-coders build a site. And that's where WP is way more attractive than WB, because WP has tons of bells and whistles (addons, themes) while WB has almost none in comparison.
You say WB is a basic platform for developers. It has become that now due to the fact that it lacks a repo of modern ready to use addons. So indeed you have to be a developer to use WB as a start. But with WP you can build professional sites without being a coder. That's the big difference.
WB however shines in being a lean, user friendly, logical system, while WP has lots of things that are not so lean and not so user friendly. But in the end, it has much more (potential) power and possibilities than WB in its current version.
I do hope WB will see a revival and become a modern platform with pontentially a large repo of addons.