I suspect that the injection systems do something somewhat
like what you described, but exactly the opposite.

A sequential system fires the injectors individually, but
that doesn't mean it isn't firing them simultaneously as
well. At low RPMs, each injector is firing individually
just prior to it's intake port valve opening. In this
way, at low RPMs the fuel is perfectly metered and in the
finest mist possible, thus reducing emissions.

As RPMs rise, in order to deliver the correct volume of
fuel, the injectors have to stay open longer. On a
sequential injection system, this translates to starting
to inject fuel *earlier* in the cycle. At maximum load,
I'd imagine all the injectors are firing continuously
regardless of if they are sequential or batch or all
firing together like the k-jet system.

When people modify their cars to produce more power
than their stock injectors are capable of delivering in
the form of fuel, there are several options available to
them. They can boost the fuel pressure (rising rate
fuel pumps / pressure regulators). The stock fuel
pressure regulator does this to some extent already
(that's why they've got vacuum fittings, I think) but
in this case, they're boosting the pressure to beyond
the rated pressure of the injector. Another option is
to install larger fuel injectors, but as you pointed out
earlier, these are less able to correctly meter lower
volumes of fuel so emissions and idle suffer. The
last option is to have another set of injectors that
are only used at "crazy time" levels of power. I don't
think any stock cars ever use the extra bank method.
chris