Thats the idea, local lawyers know far more about what will stand in the courts than global 'consultants' that are just ripoff artists. Tax authorities can say this and that but its the local local laywers and experts that can know what are the bluffs or just nonsense being said by authorities just to increase tax revenues. I would bet that a lot of the countries that say 'foreign source income is tax-free' or 'capital gains is tax free' will be indeed tax free for a trader (it will hold up in court), even if the tax authorities spout nonsense about being 'labor income' or whatever they say to scare people into paying more
That can happen although it's a 50-50% chance and if you lose you usually owe them a 50-200% tax penalty plus interests which can hurt. I agree with you but do not think that I've only asked PWC and KPMG. If you go back in this thread then you can see that I've asked local advisors in many countries. I think 8 or 9 in Switzerland alone about the lump sum tax.
You know, most advisor says that if you make lot then they'll find a way to tax you. If you don't make much then you're fine in whatever territorial tax country but then why bother going anywhere? Go to the UK, get a job and do some spreadbetting on the side and it's tax-free.