It's not optimal. Edit: Imagine trying to heat e.g. a pastry carefully. 10 seconds at full power is enough to make it start boiling, partially, because of the uneven microwave radiation pattern. Other parts will be cold.
I've never tried a Panasonic inverter-style microwave oven, but I imagine it would solve this problem. It would be able to run at like say 30% for 30s while rotating the contents.
I have a Panasonic inverter microwave, and it does solve the problem quite well. The standing waves aren't solved, but the lower continual heating lets the energy conduct in the food without overheating parts.