For Germany this in not true, I have direct experience of this. Your income is really high at 150k€, even taking in account all taxes you pay if you’re self–employed (plus insurances, social security contributions, etc). You’re way above what you would get from the German market, unless you go into management.
Is it his responsibility? If some countries have a better tax policy, why should he not take advantage of it, and ultimately end up in a situation that benefits both the employee and his company?
If you are actually talented, have a good work ethic, and the track record to show that then get a job that relocates you to London.
That is your only option if you want to stay in Western Europe as a SWE long term.
This is terrible advice. Source: been there, done that (worked my ass off to waste half my TC on taxes and the other half on cost of living). I ended up moving to a low-tax Eastern European country so I can actually feel like I'm being fairly compensated for said talent and work ethic.
I don't actually see how your advice improves the situation - the net disposable income you'll end up with is about the same you'll have from being lazy in Western Europe - except at the very least, some Western European countries are actually nice to live in. If you're gonna be poor anyway, may as well be poor in a nicer place.