The United States is not a welcoming place for EU citizens. Immigration is strictly limited, the procedures expensive and time-consuming. If that's the bar for the UK government, the grandparent poster is right: it's not going to be worth even looking at Britain.
To put it another way: if working in London, New York and San Francisco are going to be equally difficult to arrange, I'm not sure why anyone would prefer London. Housing is as expensive as NY or SF, yet wages are much lower. The weather isn't great either.
These can be valid points for some, and carry less weight for others (say, if you live in Paris and are offered a good job in London, and they help you deal with the visa stuff, for most it's probably also nice to be able to visit Paris much more easily than you could from NY or SF.)
At any rate, "not sure why anyone would prefer London with the post-EU laws" is very different from "they decided they don't want me because they're not in the EU (even though there might be an otherwise nicely sounding arrangement available for me)."
> if you live in Paris and are offered a good job in London, and they help you deal with the visa stuff
Note that the freedom of movement in the EU means there isn't any "visa stuff" to deal with.
An EU citizen moving to the UK needs to fill in a form, to get a "National Insurance" number. The same would be required of a British citizen that didn't have one, for example if they'd been born and lived overseas before moving to the UK.
There are no other requirements that don't also apply to British / resident people moving within the UK.
Well, yeah, but here the entire discussion is about UK's exit from the EU, at which point freedom of movement in the EU doesn't apply, I think. So I was describing a hypothetical future situation where you would have some "stuff" to deal with.
To put it another way: if working in London, New York and San Francisco are going to be equally difficult to arrange, I'm not sure why anyone would prefer London. Housing is as expensive as NY or SF, yet wages are much lower. The weather isn't great either.