For the rest of us we don't care where the devices are made - since there is a global economy. If 'Mercian stuff is really the best, then it would be the most popular and people would buy it from there anyhow.
I think it's a bit more complicated than that. To an extent you are correct, and you are absolutely correct that competition is good and keeps people on their toes. You only have to look at industries where competition is poor to realise that even cost isn't the only factor - quality can suffer even if prices are still high.
However, I don't think you're quite right to say that people will buy "the best" regardless of cost. There are certainly a few people who do that, for various values of "best" which are not exclusively down to exquisite manufacturing quality control but may also include environmental impacts, ethical employment practices, even vegetarian credentials, but the bulk of the population (I'm guessing) considers price above everything else, except for a very few select products, of which the iPhone is probably one.
This is why people still buy Danish bacon in the UK despite UK welfare standards being higher - it makes UK bacon (generally) more expensive. It's why people buy Dacias instead of the equivalent Renault model, and fly EasiJet instead of Lufthansa, and it's why Dyson moved his factory out of the UK.
In other words, given two equivalent products (let's say 500G of smoked back bacon), most people won't even look for the little red tractor on the packet in Morissons - all the packets look the same and all the bacon looks the same, but some packets are slightly cheaper. Get those. As you say, "we don't care where the [stuff] is made".
People like Trump see this, and see that the only way out since a large part of the cost of home-manufactured things is higher worker welfare standards; i.e. better wages and the average UK or US worker couldn't even afford to travel to work for the sorts of daily wages some eastern-hemisphere workers are paid, is to make imported goods as expensive as home-produced ones. This leads inevitably to tariffs.
Tariffs are why Welsh lamb producers are worried about Theresa May's apparent support for a "hard" brexit; the only thing that makes many people buy Welsh lamb in the UK and in Europe is that the EU has a big import duty on New Zealand lamb. Take that away and NZ lamb becomes so much cheaper than Welsh lamb that the market will probably collapse - just look at what happened to Welsh lamb producers in the 1970s before this tariff was introduced. On top of that, chances are that the import tariff that catches NZ lamb going into the EU will now catch Welsh lamb going into the EU and you have a doubling of the effect.
I really don't like the fact that Marks & Spencer now makes their underwear in Thailand (or somewhere similar - I can't remember) and the factory near where I used to live near Worksop closed as a result. I find it amazing that they can now sell such items in the shops for the same price I used to pay for "seconds" at the factory shop, but I can't deny that having twice as many pairs of socks available makes keeping on top of the washing easier!