In general, men who have levels in those ranges & who are experiencing low Testosterone symptoms will already have difficulty putting on muscle mass, maintaining it, and keeping fat off due to those factors and a lower metabolism. So moving yourself back to a stronger range & removing those symptoms should provide a noticeable increase in effort to improvement ratios for your physique.

What you say is also true, that there is less defined ups/downs & additionally less impact from lifestyle choices. The variance throughout the day, alcohol, low sleep amount/quality, lacking hormone building blocks like good lipids/ZMA are all things that also cause variance. By using TRT as you suggest, this variance is greatly reduced & your body has a lot more consistent of an experience which does lead to more stability & improvements during recovery from the gym.

You will also find that not all parts of the body benefit equally, which may or may not be a good thing for your goals. You tend to have more androgen receptors in your chest/upper back/traps etc. If you struggle in those areas already before TRT, you will probably be quite happy with the aid to those zones. Some men respond extremely well on TRT in those regions.