I would argue that this turbo is well within hiflow territory so it is probably redundant (on cost/benefit but not useless or hopeless) before it starts.
To me the compressor isn't flowing significantly that early like the other more slippery GTX compressors so a smaller housing would give a bigger shove down low. Nothing earth shattering in saying that. The peak power everyone was expecting was within reach of the 0.63 so it makes sense this might have been the best housing to try.
Why Garrett chose this compressor has a lot to do with someone wanting 450hp, 500hp, 550hp (or whatever steps each compressor offers) after all they all run the same turbine wheel.
What none of us know is how it drives, dyno prints aren't worth a lick of spit for telling you how much better this thing runs on the road for rolling response hence I would just drive the thing and enjoy it.
I would certainly check for boost leaks because they are highly parasitic.
If I was made of money I would consider buying a 0.63 housing and a retune but given the time taken to get it to this point there would be no urgency on my part unless the workshop was going to make up the cost of selecting a less suitable actuator and seemingly putting work on the car on the backburner.
Ultimately all our conjecture is sometimes a bit of a downer for the OP and we can lose sight of the fact that we will never be 100% happy with a setup because someone else will tell you they can always make more power, come on earlier or do something better.....drive it enjoy it and see how you feel in 6mths.