The bottom mounted DHW coil is always in the colder part of the tank so if it used to take heat from the house for frost protection it will not cool all of the DHW tank - agreed there should be software options to change this
This HP is much greater capacity than 8kW nameplate implies and I think this is a confusion of the rating for HT pumps. If you look at the performance table unlike normal 8kW heat pumps that start to reduce output in negative outdoor temperatures it remains at up to 8kW and not reducing to 5kW output as is more typical so there is a fall back situation to keep the house warm (albeit at a cost by using high flow temperatures). The high temperature operation output can be up to 11kW with 4kW consumption. This rating of two stage heat pumps is discussed elsewhere in the forum. So it is not a typically rated 8kW more like a 11kW.
Why it is advertised at 8kW? I do not know. Maybe it is for certain market requirements where keeping below the maximum load rating is important.
The same goes for the software changes. I do not know why the Samsung HT is like this but it may be due to protection of the safety systems running at up to 70C which you do not need.
Maybe you can get an exchange from your distributor for a Samsung without HTQ which are significantly cheaper, the controller would still be compatible and it would not have these problems for your installation?
The world of domestic heat pumps seems to be developing fast especially for retrofit programmes, what I have today will probably be outdated in five years. It is all just an experiment but working out so far…fingers crossed!