If ^^this is what you meant, then I'd agree. No point in shutting yourself down permanently to just go on TRT and raise it a couple hundred. The difference would be hardly noticeable.... Though, a cycle will put mass on.
Genetics play a major role here. What makes one lose it, is the tanking of Test levels once you come off, and the body needs time to start natural production again. Guys will say they were spinning their wheels getting big then losing it while cycling on and off. Only to start retaining some of it when they decided to blast and cruise. Because the Test levels don't tank.. On say, 500mg/week, they'd go from somewhere between 2200-4000 down to 800-1000. When one comes off, they'd go from the 2200-4000 down to almost nothing. Depending on genetics, one might retain alot, one might lose alot. More likely the latter. Since most are not genetically gifted.
Either he's genetically gifted (which I wouldn't expect that for yourself), or he's blasting and cruising, or perma blasting.
Humans all have the ability to build muscle, but to what extent? What do you mean by "fair bit"? If it's something that most would consider impressive, then no. If it's something that looks fit, but average, then yes. Though again, genetics play a major role.
You'd go from 600-upwards of 2200-4000(depending on your body's response). Yes, you'd see a difference in performance, recovery, strength, and size. Though again, genetics plays a major role.
You wouldn't want to add dbol into the mix without first knowing how much your body coverts test to estrogen. Genetics play a major role in side effects as well...
One may be able to handle high amounts of estrogen, and not get gyno due to aromatization. Others may not be able to handle high estrogen, and get gyno, though they don't covert test to estrogen at a high rate anyways.... Others may covert at a high rate, and get gyno easily, which means they'd need to keep their test dosage to a level that doesn't cause the high estrogen effects, and introduce another compound that doesn't aromatize to estrogen like dbol does, or take a massive dose of A.I. which would be unhealthier than using a different compound for strength and size.