Those who say we should just "bear with it" as Tesla's a startup and deserves our support clearly haven't been owners for very long. The fact is, Tesla service and support used to be excellent (not perfect of course, but still better than traditional dealerships). Now, some 6 years down the line, things have gone down the toilet. Why?
May be because in that time they have sold 6 years worth of cars?
It might be as well to clarify what you regard as 'service'. My view is that 'poor service' covers all engagement with a supplier. If you are more focussed on 'After Sales service' or 'warranty service' or just 'routine servicing' then that would be slightly different.
I have indirect experience of Tesla since the roadster was released in the 'States. The decline in 'service' may track very closely the increase in sales with the M3 and possible decrease in margins that often goes hand-in-hand with higher sales volume products. It is quite likely that an individual M3 customer is less financially interesting as a prospect than an MS customer.
It seems generally accepted that Elon has been under intense pressure to show profit, and that means focus on selling. There is no defense offered here for lousy service, and the idea of 'cutting slack' isn't one I readily subscribe to, but there is no sudden point at which the Roadster building garden shed business can suddenly and irrevocably become a flawless world class EV manufacturer. There will be ebbs and flows in their offering, and right now we can see a monumental lack of structure in the UK. If Brexit ever happens, that may change further. Driving on the wrong side makes us different again.
There must be a conduit for genuine customer experience to feed back into Tesla at a high level to direct their policy if they intend operating in the UK. They are at liberty to enhance UK support, or pull out completely. Their commitment to build in Germany is a clear statement of where they feel there is a more stable environment in which to build.
I don't think we need to bear with Tesla. Sure, make a noise when things go wrong if that makes sense. But we do also need to recongnise the realities at play.