I need to switch between doubles and singles and I find having everything on 11" centers makes swapping out gear trivial. Adding a single tank adapter to my single tanks gets them on the 11" mounting so I dont mind using STAs. However, STAs cost way too much, so I just make my own. I suspect manufacturers/distributors try to make up for lower profits on backplates through higher profit margins on single tank adapters. Pain to make, so I don't advocate this, and I don't make them to sell.
I'm not tech or DIR, DIO (maybe) solo is closer to the mark. I just need to be able to switch gear out, I don't find back plates to be uncomfortable in or out of the water, and I wish I would have done that from the beginning. BP/W setups offer modularity and consequently facilitate transitioning to different diving conditions: dry suit, wet suit, no suit, this bladder or that bladder, this tank or that tank, while still keeping the diver interface (harness and backplate) similar.
They cost about the same upfront, and can be cheaper in the long run if you plan on adding options (cold/colder water diving, longer/deeper diving, ...)
I also dive a Zeagle Ranger (a soft back version of a bp/w setup), and overall its a very nice solution. Still, I would rather have just bought a bp/w if I could do it over. I just moved over to BP/W setupt from the Zeagle (and a jacket/bp before that), so I have less experience with BP/W than without BP/W.
P.S. If you want a cheap single tank solution, something like an oxycheq signature bladder (30# or 50# lift) at a cost of about $250 mounted between an old style plastic backplate (1970's jacket bc backplate) and tank, rigged with a hogarthian harness makes an awesome single tank setup imho. Super comfortable and you can upgrade to a real bp later if you go doubles, and the plastic bp aren't hard to find for free (unless, of course, you are looking). I have a setup like that rigged hogarthian style with super soft nylon cargo restraint webbing, 30# bladder, and it is super comfortable for warm water diving. Very "old school": I use it when diving with my vintage gear even though it is more modern with the inclusion of the rear bladder (looks way cool though, from a minimalist perspective, and is VERY practical). I would trust it as a modern single tank solution as well (with good upgrade potential).