I don’t think that’s the case at all?

If you look at any modern voltage regulator it switches in the megahertz range with variable pulse width and interval. This is all controlled in the digital domain (lower end ones do use analog control loops, but higher end do not).

Above the megahertz level switcher everything else is just capacitors providing low impedance at frequencies into the high hundreds of megahertz (and at gigahertz it’s on-die capacitance).

‘too fast for digital’ makes no sense when talking about control loops, digital is faster.