Not sure. I've heard from a lot of start ups recently moving from London to Berlin. I doubt many start ups have the complexity of the tax system high up on their list. It's about finding talent (where Berlin improved a lot over recent years) and to some degree costs (where parts of London have become extremely expensive).

But it's probably mostly network effects. The US has an extremely complex tax code and SV is one of the most expensive places to live. It still remains a favourite among founders.

True. They try to fish startup founders by running corporate incubators but they will make sure that you won‘t get a high exit. If the idea works you‘ll get a job offer. If you decline, they will drop support like a hot potato. And because they know all insights, no other competitor is interested in you anymore. It‘s kind of a faux startup culture just to sell some „coolness“ to attract people to big corps.