The way you phrase your question is likely to get you a fairly clear response that scuba won’t be the answer. I am no expert but I highly doubt it will “get your muscles back in shape”. Also the relief that the (fairly temporary) weightlessness under water gives versus the work required to get in and out of water is out of proportion. Honestly, the risk of getting in and out way outweighs the benefits unless you are able to work to get the back in shape in other ways.
Scuba per se is not that great work out (in water). Indeed, I have noticed some athropy with some muscles since taking it on. It also strains back to some degree eg you need to arch your back to stay in trim. Kicking in more demanding conditions puts a great strain on my back some days at least (not that one needs to choose to dive in those conditions with a bad back). The work out really is on land, and it’s exactly the type of work out you do not want with bad back – load bearing, twisting and bending with a weight on you, yanking yourself up, possibly handling weight on uneven or moving surfaces and sometimes impacts (jumping in) etc. All no-no:s for crappy back.
Not to be a drag because it’s a great sport but I would say that unless you are dying to dive, scuba would definitely not be the first sport/recreation I would pick as a back rehab. (Swimming as you know is great). I am not talking out of my a$$, as I am recovering from a severe back injury myself, and I curse daily that I am so addicted to scuba that I can’t quit thinking of ways to abuse my back again the day I am cleared to get into it. It’s a great motivator but help yourself while you can and pick something more sane if you can! I certainly feel your pain about boring mini-walks, back and forth swimming and doodling this and that when wanting to do real things, hang in there!