You make a good point, so that could be a fiscal anchor in itself. We will ensure that our debt does not exceed a level at which we have to pay more than x per cent of our tax revenues towards interest.
That's why I am saying that if a fiscal anchor is necessary, or is useful at least, the choice of a fiscal anchor is up to the government. Multiple fiscal anchors can be chosen.
To get back to a point you made, if the government spends and incurs additional debt to make the economy more productive, eventually that will reduce the debt-to-GDP ratio, other things being equal, because that will lead to more economic growth, which will reduce the relative size of the debt.