In your view, what are the disadvantages?

The primary disadvantage is the high cost of housing. That is the "root cause" of many other knock-on problems that are caused: inappropriate living space for some people, some with long commutes, some people feeling like they or others they know don't really live in London but instead in some dormitory town outside the M25. Until we can get the cost of housing under control there are all sorts of people who I would like to live here and "be part of it" but whose lines of work don't pay them enough to.

But this problem arguably exists in every Western city at the moment. I have my own pet policy ideas which I won't raise here. I will say that this problem seems to be markedly worse elsewhere, for example in American cities, Australia, Canada and also even on (western half of) the continent.

EDIT: Also pollution levels

Let me tell you a story. I am a linux kernel level developer. Even better, I have implemented multiple windows drivers in my life. And I have tried to implement application level firewall for linux as after 20 years there is still none around (I have abandoned the work as kernel was protected against my method). Proficient in C/C++/Rust/Go/Java/Python/Assembly/... or to rather say it in anything in Tiobe, even Prolog.

I have a nice job at my country at 2250 euros / month (which is twice the average salary) and I was asked to work for some company where I would get around 3000 euros/month.

And now it gets interesting. On interview, they will ask me various questions about my work that should theoretically be memorized by anyone comming from the school education. I have 25 years of development behind me and I dont have the "stack" to remember everything. And I am already decided to give them "fuck off" once they start with the theory.

On other side, I have a child from previous marriage and I will not leave the country for the sake of the team. Child development is more important to me.

So, I am over-competent engineer, bullied by idiotic recruiting, fixed in the position that I have, unable to relocate due to life circumstances. And now "moving to London" is a thing. Yeah right.

Your competencies might be real and correctly-assessed, but from your description, you sound like you might be difficult to work with.

I don't mean to extrapolate from Internet-rant to presumed-reality, but this is a common pattern, so maybe it's worth mentioning:

I can teach a person Prolog. Any reasonable developer can teach themselves Prolog.

I cannot teach a person, nor have I ever witnessed a person self-educate on a short (employer-relevant) timescale, the willingness and propensity to work cooperatively and constructively, if it is not in their nature at interview-time.

Sometimes the latter is much more important than the former.

Negativity is infectious, and people naturally steer clear.

This seems to be a really difficult point for some people to really wrap their head around. You can be as intelligent as you want, very rarely is someone going to hire you if you seem unpleasant to be around.

You could always pick one language to be an "expert" in and just study up on the book learning for that language for your interviews. I've shipped products in a dozen languages myself, but for an Android interview I'll only claim to be expert in Java and Kotlin, for iOS I'll only claim to know Objective-C and Swift, and for server I only claim to know Java and Go - even though I've shipped PhoneGap and React Native JS mobile apps, JS Node servers for startups that got funded, Amazon lambda functions triggered from Unity, etc.. Just not up to speed on the book learning/pop quiz/mind teaser type questions I'd get for those.