As others said it's efficiency, not abuse. Would it change anything if you used 3-4 relatively cheep vessels to complete all those missions? You would still complete them within budget and probably it wouldn't take you much longer. Even "lost of control" wouldn't change much if the same design could be used for all of this. Now, my point is - you can do in ONCE. If I understand correctly (I'm still new to this game) you won't get the same contracts to Mun and Minimus again. And for other astral bodies you will need to plan differently to accomplish similar achievement. It definitely would be abuse if you could do it over and over to raise funds and science.