It's more a matter of efficiency than throughput. Mark-one googling suggests that a shower head might have a flow rate of 2 gallons per minute (0.125L/s). Suppose that the incoming water supply is at 10C, and the target hot water temperature is 43C (110F) for a shower.
The necessary heat flow rate is 33C * 0.125L/s = 4.125 kilogram-degrees per second. Multiply that by the specific heat of water (4184 J/kgK) to give a net energy flux of 17.3kW. On a 240V circuit, that would require 36A of current for electric resistive heating, a hefty circuit indeed.
I'm having trouble sourcing a reliable comparison, but the calculated 17.3kW draw appears to be larger than a typical natural gas stovetop with all burners on.
> There's just no return there for a big investment. And I can never have solar so free electricity is not a thing (I live in a big city and don't own the roof of the apartment building)
You might not personally have free electricity, but utilities are experimenting more with time-of-use billing. Hot water tanks allow heating demand to be time-shifted from use.
The finances clearly don't make sense for you right now, but there might come a time when electricity at some part of the day is cheaper (heating equivalent) than natural gas.