Princes Street hasn't been "all that" since around the time that Renton sprinted out of John Menzies (much missed, or, at least, it was at the time).
M&S? OK, it has a food hall, but ever since they squeezed 2 into 1, it's clear that they'd much rather you went to the Gyle if you are clothes shopping.
Frasers (as was), Debenhams, Jenners? Old buildings with floor layouts that shift randomly in the space-time continuum and are far too easy to get lost in and never find what you were looking for. Arguably for Jenners, that might be part of its charm, but I'm never sure who its market really is. I suspect that tourists maybe make up a perhaps worryingly large proportion of its custom, rather than regular repeat local shoppers?
The Debenhams building is ripe for gutting completely on the inside, and rebuilding with a more consistent floor plan, while retaining the facade, if you ask me. It could perhaps make a great city centre IKEA (there is at least one in England somewhere, because of local out of town planning restrictions), with home delivery for bulky items, perhaps even by cargo e-bike for suitable items?
BHS (as was): this was actually a fairly sensible building layout, and, yes, fairly impressive for the standards of its time. It just didn't sell what many people wanted to buy.
So, what are we left with? Yes, Mountain Warehouse for the occasional useful thing (although not always the best quality, buyer beware), the "real" outdoors shops on Rose Street (albeit still with very "traditional" opening hours (Don't you know we're all at work during the day, and Decathlon is open until 20h, and is often "good enough"?)), Primark for cheap black t-shirts (you can never have enough, although many other colours are indeed also available), the Apple Store, and a couple of bookshops.
For literally almost everything else, it's off to one or other of the supermarket superstores out towards the edges of the city. Or the internet.
Actually, maybe what Princes Street needs is a bike shop?
And, yes, some nice pubs and pavement cafes and restaurants to take advantage of the views over Princes Street Gardens on summer evenings?