I think the genetics play important role, but on the other hand, everything, that is not a bone, can be altered in some degree by the hormones... For an example, now I have the slimmest waist since I grew up and even and year ago it looked close to impossible for me to have the measurments I have now, and I am transitioning only for 13 months and I am 33 years old... So mine from year ago and now are as following:
Bust: 94 cm (37") / 103 cm (41")
Underbust: 85 cm (33") / 80 cm (31")
Waist: 83 cm (32") / 70 cm (28")
Hips: 93 cm (36") / 99 cm (39")
Thigh: 55 cm (22") / 58 cm (23")
Height: 181 cm (5'11,5") / 180 cm (5'11")
Weight: 67 kg (148 lbs) / 76 kg (168 lbs)
As you can see, I am much heavier now, but have slimmer waist and more feminine proportions. I am pretty sure, that if I succeed to drop at least the weight I gained due to HRT, my waist will be at 2 or more inches slimmer, so I think it is a good idea if one just be patient and wait the hormones to do their work and then, if not satisfied, to think about a surgery... Just my five cents