Not for the businesses involved it isn't. especially small businesses and mid size ones where the UK is a market but not key. Sure, Amazon will be unaffected (though more dependency on Amazon is bad period) and yes the issue of handling surcharges will in theory be removed (though that will be replaced with higher prices as companies will have thinner margins due to paperwork and staff that were not needed in the past for one country/market). In fact it's entirely possible that the surcharges that already exist will be an expected transaction for the business and will be, of course, past onto the consumer with a profit margin attached. All that, plus, inevitably, less choice. Not to mention the other issues for UK exporters which will hurt small and mid sized companies disproportionately .
Yeah that's what I said with the surcharges, it's the logical outcome. But I'm talking from the consumer pov because I don't really care about the business portion, they will adapt.