Stockholm has a thriving tech industry and not really low tax rates. Tech can easily headquarter in a low tax domicile and employ most people in another country, all bigger companies are already doing that. I don't think that the difference in income tax explains where tech companies settle, it'll be much more dependent on availability of talent (and how easy it is to get people to move there). That's why Amsterdam, Berlin and Stockholm are so successful, they are all within the EU and have a good reputation with internationals.
Yeah, but a huge problem with finding accommodation for it's recruits. In contrast to Berlin it's impossible to get a first hand rent contract. A second hand is going to be super expensive and buying somewhere somewhat central is ridiculously expensive.
Focus on economic output, that's what's most important to the company. Time in seat is a useless statistic, may well be the employee has been lazy for 6 hours. Read https://news.ycombinator.com/item?id=9360061
Large corporations don't want their headquarters in Berlin for tax reasons: There's a reason they're all moving to Switzerland.
The tech scene in Europe is very scattered.