I wouldn't say it's a toolbox, it's just another browser with some more sugar strapped to it out of the box. Coming back to your smartphone analogy, it's just another smartphone with more stock apps that many users don't want at all.
You mean like pre-built toolboxes have some tools many people don't really want? Good thing people can choose the toolboxes they find the most ideal, even if it contains only a hammer and a duct type and a lot of empty space, isn't it? :)
When Opera switched from Presto to Chromium, it was about as fast, but it was much lighter. Yet, almost every Opera fan/"customer" at the time was pretty mad. It was not because they were attached to Presto, but because of the huge feature depreciation. It's the features what made people use Opera until its 12th iteration, and some even use it today despite it having huge issues chewing through the bloat of JS on some sites.
Yeah, they really stripped it down... at least it put an end to all the fanboy gangs who used to jump into any browser-related discussion, trying to convince everyone how Opera invented everything including tabs (it didn't invent tabs), and how other browsers are nothing but knock-offs that don't even have a torrent client built-in ; )
(No offense to Opera supporters - I used it on PC for a while and it worked very well esp. on slower machines, and I use it on Android to this day - but this was annoying like hell)
The point is that Vivaldi is a toolbox. Some people like toolboxes.