My credentials: In high school and university, I used WordStar 3.3 on CP/M. Today I'm a technical writer. I reluctantly stopped using WordStar when WordPerfect pushed it off the stage.
It's hard to state advantages WordStar has over modern editors. Maybe looking at it in a historical context helps.
User friendly: WordStar was for non-technical users. "User friendly" was frequently abused in industry marketing. The implication of user hostility was real. You often had to assemble your computer from a kit. I don't mean plug in an SSD and a graphics card. I mean solder chips onto a board and cross your fingers. A non-techie could use WordStar out of the box.
Power users: Newbies dedicated 1/3 of screen space to an interactive command list. Power users used all screen space for text.
WYSIWYG: Editing and formatting were traditionally separate programs. Competitors sorta kinda integrated them. WordStar seamlessly combined them for the best WYSIWYG that display hardware allowed.
Flow: If there is a genuine advantage, this is it. WordStar was for professional touch typists, like secretaries and writers, paid to bang out words all day. But keyboards were simpler, typically 50-60 keys. WordStar used only Shift and Control as meta keys and laid out its keyboard commands intuitively. WordStar let you stay in the flow to get to your final draft quickly.
Adaptable: Computer, printer, and communication hardware rivaled the Cambrian explosion in variety and incompatibility. WordStar worked predictably on serial terminals, dedicated displays, and daisywheel and dot matrix printers, serial or parallel, one floppy or two.
Ecosystem: MicroPro and third parties supported WordStar with many add-on applications for spelling, mail merge, and so on. Yes, spell checking was an extra.
Nostalgia: WordStar pushed the envelope in its day. Comparing it to today's editors and word processors, WordStar is quaint. But maybe since then we've forgotten some important reasons about why we use computers. WordTsar might be a good reminder.