As I said, I don't hold Merlin accountable for the specific issues, with the responsibility there falling to the relevant company, but they are still the ones signing off on the attraction and accepting the state that it is in. With their own reputation as well as Derren's on the line, I would expect them to have had fairly extensive testing procedures with reasonably high standards to satisfy before allowing the attraction to open. Perhaps they thought they did, although with hindsight it's evident that maybe more could have been done, but one week of technical rehearsals, opening without all the VR incarnations and some headsets not working doesn't really support this.
To me this instead signals that there was commercial pressure behind the scenes just to get the attraction in a minimally acceptable state to open, although in this case that still made for a somewhat impressive attraction on a good run-through probably because of Derren's influence of those standards and the fact the whole experience breaks-down even if just a minor element isn't working. Added to this you have Figment Productions themselves publicly admitting the technology isn't yet available to deliver the experience the creative team wanted (whether this is in reference to the VR content and/or suitability of the HTC Vive in a theme park environment is unclear), something I'm sure they would have expressed to Merlin but it was decided it did the job. This feeling of pressure also comes from when the attraction did eventually open, with it being just prior to the school summer holidays, an undoubtedly key period in any theme park's calendar and so understandable that a park would want its new major attraction open in time. Perhaps this is why we saw a shorter period of technical rehearsals than we may have expected, with Thorpe/Merlin taking the decision that it would rather have the attraction open for peak season (and could market it being so) than allow for a longer testing phase that may have identified some of the issues that surfaced once the attraction had been operating for longer.
I never expected the attraction to open in a perfect state with no downtime, Merlin were of course attempting something genuinely innovative which I won't criticise them for, but I would want to feel satisfied that it was opened in the knowledge that it was complete and wouldn't have any major or experience-ruining issues and for the reasons above I don't. There are of course worse examples of theme park operating companies in the world than Merlin, but there are arguably also those that are superior in terms of giving creative forces more control over their commercial counterparts.
Mainly comparisons are drawn with Disney and Universal because these are the companies opening state-of-the-art dark rides (as well as being the closest in terms of attendance), and perhaps therein lies the problem; these are parks which are open all year round, as well as appealing to a large and consistent international market, and so have a more fluid investment cycle as a result. When Merlin assign a theme park high capex for a particular year, this isn't something that can be changed in the late stages without having knock-on effects to the expenditure cycles of other Resort Theme Parks in the group, and so they're therefore committed to opening an attraction in the year that has always been planned. As we've recently seen with delay of Fast and Furious at Universal Studios Florida, these other companies can delay an attraction without there being too much fuss. Although it may have meant DBGT opening in a more impressive/consistent state, I can't imagine such a delay would go down as well in the UK market. Regardless of all this, you could make the argument that a comparison with these two companies is flawed from the beginning with Disney's attendance far great than Merlin's, with Merlin's then only exceeding Universal's because of its other sectors (primarily Midway Attractions), but that's not a discussion for here.
I come back to my point of these issues being understandable but not entirely excusable, in my opinion. While I enjoyed my experience of the attraction, to me it is currently tainted with the knowledge that it could be better.
Naturally we'll all have different opinions which allows for healthy discussion on a forum such as this, and I by no means want to force my pessimism in this case upon those who can currently look at DBGT in a more favourable light than others