The thing is, soft openings do actually work! I remember being able to ride Mission:Space in Epcot, around half a year before it was due to open. It was mental, almost too intense at that stage. After the ride opened, it was toned down (subsequently again a year or so later) due to the feedback from guests.
Now in Europe and America, it works. They usually build year round aiming for a peak season opening. Therefore can allow extra time for soft openings and stuff.
It's a lot harder over here. The only way it would work is if Towers began every build about 2 moths earlier to allow for this time. But then the issues are, it costs them more money for longer construction, and rides wouldn't open at the start of the season. So until UK parks open year-round, I can't see it happening really. As much as I think it's a good idea.
"It would be spiteful to put Jellyfish in a trifle..."