genocide vs ground assault

[Q]

Puke this works fine for one or may be two enemy planets especially their home world, but if they have already 5-10 colonies I would disperse my fleet completely and be very vulnerable to counter attacks. And to blockade a new colony with 10M population and 1-2 facilities with three of my costly ships seems not very efficient to me. So in this case I eliminate all their minor colonies first one after the other with my entire attack fleet and then as the fatal blow I blockade their homeworld and demand surrender. However there are now races in the game that will never surrender!