Good practice to do one major thing at a time, so that pilots can confirm correct selection, correct movement and correct final position. If you get an uncommanded roll after dropping gear and flap together. which service is causing the uncommanded roll?
No need to rush in aviation if you are doing it right. So why put your hydraulic system to maximum load if you don't need to? A good pilot will respect their aircraft mechanisms.
In a go-around, as you know, the call is "Go around, flap" <select flap> then read out FMA. Then PM will call "positive climb", then PF will call "gear up", <select gear-up> , so the two things are not simultaneous and by the time the gear is called for the flaps will have finished moving.