What you’re saying is true for long term abuse of steroids, but a modest one month cycle of deca for recovery from surgery will not result in any of these side effects in the vast majority of cases. Sensible tapering would make them even less likely.
As others in this thread have pointed out it’s not necessarily a good approach for healing a tendon, and could be counterproductive.
Back in the day when designer “pro-steroids” (basically tweaked pro-hormones that metabolized into anabolic steroids in the body) were widely and legally available from supplement manufacturers, I had a bone graft surgery scheduled and wrote to the chemist who had developed one of the better products to get advice on a cycle for my recovery. This is anecdotal of course, but my surgeon told me that when she was fixing up the bone she realized it was in worse shape than the MRI had indicated and she puts the odds of success at 50/50. She was amazed at the speed and completeness of my recovery. I still have Frankenstein scars where the stitches were because my skin had “healed so quickly” that the stitches were difficult to remove and left gnarly holes.
I like to think that the supplement tipped the odds in my favour. Despite the well-established benefits of anabolic steroids on bone healing, the stigma around them means they are almost never prescribed even in bad cases. YMMV, but other than a few friends commenting that I a bit of an asshole while on the cycle (which could have just been the misery of post-surgery), I suffered no ill after-effects and actually put on a few pounds of lean mass despite being largely convalescent.