Do you mean to say that you are just skipping missions and not attending them in order to spin the globe faster so research is done?
That is a bad idea. And yes, you should always be able to field a full strength sortie, even if many of your people are wounded. This is expected, and the way game was designed.
Also you do not need to be so callous as letting your people die on the battlescape. Even almost dead people will recover, and veterans are worth a lot in tactical flexibility. Hire new people AND save almost dead people, I don't see why you cannot do both.