I just replaced the motor run capacitor on my furnace blower, due to the gradual failure of the old one. It is rated 7.5 µF, 440 V. The size is kinda sorta 1 inch x 2 inches x 3 inches. It measured 2.2 µF when I pulled it out.
I remember, back in the 1970's, I had a fluorescent tube ballast capacitor, which was described as 8.5 µF, 250 V AC. It was probably 2x or 3x the size.
I really don't know if material science has advanced that much that they can shrink down the volume that much today compared to the old days? I've got to think it is cost cutting.
From what I understand, run capacitors are considered to be a consumable now, they are guaranteed for up to 5 years, and are a regular replacement item. I'd rather pay twice as much, and not have to worry about replacing it.