Yup, there are other deviations from the ideal capacitor than ESR like ESL, dielectric absorption, temperature fluctuation coefficient, non-flat capacitance with respect to input frequency, etc. Also the amount of loss is nonlinear with respect to frequency so you can't even model it by adding a simple resistor.
I just realized, electrolytics have improved over the years so the ones you replace the old ones with may very well have lower ESR and better characteristics in general anyway.