Hi Chris
I found your video sad. You have paid a lot of money for great expectations that are not being fulfilled. Like many, including me, you have gone from a Cali that worked brilliantly and expected the same from your GC, including the benefit that appears to be your main driver, the integrated "one stop shopping" of the vehicle.
I have the same Truma system but mine is Electric or diesel. I simply never let the internal temperature drop below 10degrees if I'm out and about so never have the problems you, and a lot of others, do, with the water dump. If you are off grid and do not have diesel heating then presumably you have gas? Those bottles look like 6kg and not 11kg so can understand why you would not want the heating ticking over.
Why do you travel with the bed folded up? The cooker shelf you mention and the above bed cupboards are only unusable because of the position of the bed. I do not have a GC, but my Ayers Rock is similar layout and 0.5m shorter and I've never had the bed folded up. The only reason I would do that is if I was carrying something like a bicycle, but then I have a tow bar rack for that. I am unfamiliar with the GC layout but mine has a removable separator that allows completely through access from rear doors to drivers seat without needing to undo the bed.
Access into the overhead lockers are going to be problematic regardless of who made the vehicle if the lockers are over the bed. As I'm not over 6'9" tall I carry a small folding step, stays on the bed when I'm travelling, but allows easy access to those lockers.
Taps on motorhomes are a constant source of Grumble on all motorhomes, and even some cali owners have problems (I had a tap like yours on my T6, spent more time in my hand than over the sink). They can be a pain. I believe it is a dometic made tap, although in over 60 nights now mine seems to be more durable.
I think you have the same Thule step as mine. Mine squeaks, creaks, groans, sometimes does not go back far enough to trip off the alarm, again a third party product that appears to be a problem on a lot of conversions. I find just putting a bit of pressure against it with my leg when closing helps to ensure it goes back far enough. I have asked for mine to be replaced when I trundle up to Cumbria for my first service in July and until then it's a niggle but nowt to worry about in my opinion.
Gas bottles: I have never had one given to me in any motorhome, caravan or Cali until July last year when a 6kg bottle was installed as a complimentary gesture by Adventure Leisure in Tebay. I only need to carry one as my heating and hot water does not depend on gas supply and I've got a small one burner stove with gas cartridges that can get me by should I find myself out of gas for a few days.
I hope you get your issues resolved. The frustration would drive anyone nuts.