I don’t believe that the body can grow strong due to tendon/CNS adaptations as you keep asserting. That may work for a few weeks when you begin a new exercise & improve motor skills and structurally adapt, but it will not last long. You will never get strong in the long run if your muscles are not also growing. But I think many people have vastly overestimated the impact on your appearance that gaining muscle actually has. Gaining 5 lbs of fat will make you appear much sloppier, but gaining 5 lbs of lean muscle will not make that much visual difference while wearing clothes
Testosterone can be administered parenterally , but it has more irregular prolonged absorption time and greater activity in muscle in enanthate , undecanoate , or cypionate ester form. These derivatives are hydrolyzed to release free testosterone at the site of injection; absorption rate (and thus injection schedule) varies among different esters, but medical injections are normally done anywhere between semi-weekly to once every 12 weeks. A more frequent schedule may be desirable in order to maintain a more constant level of hormone in the system.  Injectable steroids are typically administered into the muscle, not into the vein, to avoid sudden changes in the amount of the drug in the bloodstream. In addition, because estered testosterone is dissolved in oil, intravenous injection has the potential to cause a dangerous embolism (clot) in the bloodstream.