You can make the
situation better if you put two electric water heaters in series with
one another...but expect to pay bigtime in electricity.

Don't understand this 'series' comment! Do you mean parallel?

If you put the two heater elements 'in-series', even if they are now both on
at once you will get only half the wattage! So that will just take longer?

No, he means in series, but he's talking about the water lines, not the
electrical ones. If you pipe the output from one water-heater into
a second one, and thence to the shower, you get two advantages,
first, your starting supply of water is twice as big, and second, whatever
water you draw through the system passes over twice as many heating
elements, which almost doubles the heat-rise.