It is not tax competition. It's tax fleecing. The issue is that companies are paying the rates of low-tax countries while operating by and large in "high"-tax countries and reaping all the benefits from their expensive infrastructure, law enforcement, healthcare, education, welfare (to top up absurdly low employee wages)... all of which gets paid for by "someone else" (you and me).
It might be tax competition if a company that decided to pay Bermudan tax rates also had to draw all its talent from Bermudan universities, had to build their massive shipping hubs in Bermuda using Bermudan transport, had to perform their complex legal cases through Bermudan courts, had to have their entire workforce cared for by the Bermudan healthcare system (or pay them enough to go private)...
(Nothing against Bermuda, picked totally at random)
And please: capital flight being the results of abusive policy? Corporations and wealthy individuals will always try to avoid giving the fair share to the society that enabled their wealth in the first place: the case where wealth moves because of abusive policies is so marginal in the ocean of pure greed. Some countries are fiscal parasites and benefit from the theft of other societies, and this is how we deal with parasites. Should we just watch wealth evaporate away to offshore stashes, wealth that actually belongs to the people?
Given that the median US household pays about $10k in taxes per year, and has a net worth of about $120k, perhaps we also need a global minimum wealth tax of say 8% per year, with a tax free allowance on the first $100m of net worth.
The only useful number is not % tax difference between rich & poor, but % leftover for discretionary spending.
How much of your time should you be forced to devote to others - the majority of government spending is on social programs. 1 day a week, 2 days a week?
What's the fair share? I'd say it's actually far lower than current tax rates.